President Donald Trump’s use of the military domestically is dangerous and deeply misguided.

There’s growing concern that President Donald Trump might invoke the Insurrection Act to bring National Guard troops under federal control and deploy them within the U.S. This speculation may be partly because one of President Trump’s Inauguration Day executive orders, which declared a national emergency at the southern border set an April 20 deadline for the Departments of Defense and Homeland Security to recommend whether to use the Insurrection Act. That date is approaching quickly. Make no mistake: If Trump invokes the Insurrection Act to activate federalized troops for mass deportation—whether at the border or somewhere else in the country—it would be unprecedented, unnecessary, and wrong. But the president has already been increasing domestic military use. As recently as April 11th, he issued a new memorandum with yet another chill-inducing title: “Military Mission for Sealing the Southern Border of the United States and Repelling Invasions.” It’s worth repeating that there is no invasion of America, and if President Trump doubts that, he could consult himself. Last month he declared on Truth Social that the (fictional) “Invasion of our Country is OVER.” Yet under his new directive, the Defense Department is claiming new and potentially expansive powers over large swaths of federal land—including where US citizens and other border residents live. . Let’s step back a bit first and recall the military’s proper, limited role on U.S. soil, and the dangerous steps President Trump is already taking in service of his cruel anti-immigrant, anti-American agenda.

What Principles Govern the President’s Use of the Military Domestically?

When the Founders drafted the Constitution, they were concerned about constraining a rogue executive, preventing a standing (i.e. large and permanent) army, ensuring civilian government and a nonpartisan military, and safeguarding civil rights and civil liberties. From then until now, we know that a core component of liberty and democracy is the strong presumption against military enforcement of civil law—put simply, the military should not be policing civilians. For these reasons, even when the Founders and Congress have given the president war and emergency powers, it is with constraints. For example, the Posse Comitatus Act of 1878 makes it a crime to use federal military forces “to execute the law,” except when “expressly authorized” under the Constitution or by an act of Congress. In practice, this means that the Defense Department generally forbids federal troops from carrying out direct civilian law enforcement activities on U.S. soil such as surveillance of individuals, questioning and interrogations, arrests, searches, and seizures, among other things. Another key principle is civilian control over the military, which means that military troops must follow a president’s lawful orders. Troops don’t get to pick and choose which lawful civilian orders they follow and which they don’t. But for this system to work, presidents and military leaders must be careful to ensure that the orders they give are unambiguously lawful. Otherwise, they put troops at legal and ethical risk, weaken military cohesion, and undermine the constitutional design, which prevents direct military involvement in civilian life, except in the limited circumstance of genuine crises. Nor should the military act—or appear to act—in service of a partisan political agenda. Domestic deployment of the federal military is rare and has historically been reserved for genuine emergencies, like the extreme situation of an actual war, an armed rebellion, or to enforce federal laws if civilian agencies and courts aren’t functioning. One clear example comes from 1958, when President Dwight D. Eisenhower invoked the Insurrection Act (which is an exception to the Posse Comitatus Act) and deployed federal troops to Arkansas to enforce the Supreme Court’s Brown v. Board decision and guard the Little Rock Nine against a racist and violent mob. President Eisenhower acted after then- Governor Orval Faubus had deployed the state National Guard to support segregationists in defiance of the Supreme Court’s decision. The Constitution also allocates power between the federal government and the states, generally imposing on the federal government the duty to enforce federal law and defend against truly extreme crises and emergencies, while reserving police powers to the states. Normally, National Guard troops are maintained by states, under the command of their governors, as explained below. States have a critically important role to play in ensuring lawful and appropriate use of police powers within their state while safeguarding individual civil liberties and rights.

What is the Legal Framework for Domestic Military Deployment?

Applying these principles, here are the key things to know about how domestic military deployment normally works: States’ National Guard Deployment The National Guard’s normal, default role is under the control of the governor of each state or territory (or, for Washington, D.C., the commanding general of the D.C. National Guard). Governors may activate their National Guard within the state, at state expense, for purposes authorized by state laws and regulations. When National Guard troops are activated, their conduct—including use of force—is also governed by state law. The federal Posse Comitatus Act’s prohibition against troops carrying out civilian law enforcement functions does not apply to National Guard units in state status, but governors, National Guard commanding officers, and troops themselves must always abide by the limits and protections in their state constitution and the U.S. Constitution. Federal Role in National Guard Deployment Congress has enacted laws governing both federal military and National Guard deployment and conduct in Titles 10 and 32 of the U.S. Code. Title 32 duty. Under Title 32, National Guard troops can be deployed into active duty to provide support for federal or joint state-federal operations or missions that are authorized by Congress or carried out at the request of the president or secretary of defense. Historically, these federally-supported purposes include things like a large-scale humanitarian or natural disaster response, or drug interdiction. In this status, the troops are federally funded and trained but remain under the command and control of their state governor.

As a matter of federal law and practice, the president or secretary of defense can request state National Guard deployment in Title 32 status. State governors can decline such a request. If National Guard troops in Title 32 status are deployed across a state’s borders to another state, it is generally with the authorization of both the requesting and “receiving” states. Like with state active-duty troops, the conduct of National Guard troops in Title 32 status is governed—and limited—by state rules and law, as well as the Constitution and other relevant federal laws. Title 10 duty. In Title 10 of the U.S. Code, Congress has legislated the roles of the federal armed forces and the Department of Defense. Title 10 federal duty for National Guard troops has historically been rare. The National Guard may be deployed into active duty by the president under Title 10 for a federal purpose, with command and control resting solely with the president and the secretary of defense. National Guard troops deployed under Title 10 are federally funded and are often referred to as “federalized” National Guard.

Congress has prohibited troops—federal and federalized National Guard—deployed under Title 10 from providing “direct assistance” to civilian law enforcement—under both the Posse Comitatus Act and a separate provision of Title 10. The Posse Comitatus Act applies to all current Title 10 deployments on U.S. soil, and troops deployed under it to the southern border are prohibited from carrying out arrests, searches, and seizures. The Insurrection Act is generally understood as the primary exception to the Posse Comitatus Act’s prohibitions.

How Has Trump Deployed the Military Domestically So Far?

On Inauguration Day, Trump declared a national emergency at the southern border, falsely claiming an invasion, and authorized a dramatic increase in the number of federalized National Guard troops deployed to the border under Title 10. Since then, he’s also sent combat vehicles to our border communities. So far, Trump’s domestic troop deployment has been limited to support for border operations. Troops have been supporting border wall construction and materials transportation, monitoring and detection assistance, and providing logistical assistance for civilian agencies like Immigration and Customs Enforcement (ICE) and Customs and Border Protection (CBP). But his actions are worsening the conditions under which civilian border communities live. Our southern border is home to approximately 19 million people, in addition to the regular business and trade commuters who come across the border every day. In recent years, U.S. citizens and other border residents have been exposed to intrusive civilian law enforcement surveillance, aggressive federal policing, border patrol checkpoints they must pass through for medical care and daily activities, and environmental degradation from border wall construction. Border patrol agents have engaged in deadly vehicular pursuits and excessive use of force against border residents, and in one of his initial executive orders, President Trump revoked the 2023 Customs and Border Protection policy to limit these deadly chases.

What Did Trump Do Most Recently?

On April 11, Trump issued a memorandum giving the Defense Department use and jurisdiction over public civilian lands along the border—including the Roosevelt Reservation in New Mexico and excluding Federal Indian Reservations—for military activities. Trump’s directive allows the secretary of defense to identify “military activities that are reasonably necessary and appropriate” including actions to “protect and maintain the security of military installations” and exclude people from newly designated “national defense areas.” In other words, Trump is opening the door to an expanding military role that goes beyond logistical support—and potentially beyond the identified zone. The new policy has serious implications for border residents living under this expanded militarized zone, which includes cities like San Diego, CA; Nogales, Arizona; El Paso, Texas and other heavily populated, thriving communities. People in these areas could now face federal prosecution for trespassing if they unintentionally walk or drive onto a designated “national defense area.” Given the numerous documented cases of excessive use of force by border patrol agents, we are deeply concerned about the potentially dangerous consequences of adding more armed troops to border communities, in an environment that military personnel may not be trained for. Trump’s new memorandum states that “members of the Armed Forces will follow rules for the use of force prescribed by the Secretary of Defense,” but these rules may be completely inappropriate for densely populated, civilian areas. President Trump has not invoked the Insurrection Act—yet. But his administration continues to invest in the theatre of war, like wrongly invoking wartime authorities such as the Alien Enemies Act, and threatening drone strikes against drug cartels in Mexico. None of this makes us safer, and this latest move to hand over public land to the military forces our civilian communities to live in fear.

Could Trump invoke another rarely-used law at the border?

21 April 2025 Share Save Ana Faguy BBC News, Washington DC Share Save

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On his first day back in the White House, President Donald Trump signed an executive order declaring an emergency at the US southern border and directed his top officials to evaluate whether to invoke a rarely used 19th-century law in response to immigration concerns. The Insurrection Act of 1807 allows the president to use active-duty military personnel to perform law-enforcement duties inside the US. US media report that Defence Secretary Pete Hegseth and Homeland Security chief Kristi Noem, who were tasked with the assessment, will announce their recommendations later this week. Since returning to office, Trump has made cracking down on illegal immigration a central focus, and border crossings have reached a quarter-century low. But the statute could further expand the president’s powers. Here’s what to know.

What is the Insurrection Act of 1807?

The 19th-century law would allow the use of active-duty military personnel to perform law-enforcement duties within the US. This includes the National Guard – a branch of the US armed forces traditionally reserved for domestic emergencies and disasters. US presidents can invoke the law if they determine that “unlawful obstructions, combinations, or assemblages, or rebellion” against the government make it “impracticable to enforce” US law “by the ordinary course of judicial proceedings”. Once invoked, troops could be tasked with a range of duties, from quelling civil unrest and enforcing court orders to arresting and detaining migrants. Because the Insurrection Act was written in broad terms, with little specific guidance on how and when the powers can be used, it gives presidents wide latitude in deciding when to mobilise military personnel for domestic operations.

Why does Trump want to use it?

Throughout his election campaign, Trump vowed to crackdown on illegal immigration, calling the southern border situation a “national emergency” that could be better tamed by invoking the 19th-century statute. On his first day in office in January, he asked for “recommendations regarding additional actions that may be necessary to obtain complete operational control of the southern border, including whether to invoke the Insurrection Act of 1807”. The administration has already rolled out a series of sweeping measures targeting the border. These include a nationwide deportation sweep and the controversial move to transfer alleged Venezuelan gang members to a prison in El Salvador – a decision now facing legal challenges. This comes as US Border Patrol has recorded just 8,300 migrant apprehensions, marking the lowest number of border crossings since 2000. Anxiety at US colleges as foreign students are detained and visas revoked

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How has it been used in the past?

The Insurrection Act has been invoked a handful of times in American history. Abraham Lincoln used it when the southern states rebelled during the US Civil War, and former President Ulysses S Grant invoked it against a wave of racist violence by the Ku Klux Klan after the war. In the 20th century, former President Dwight D Eisenhower invoked it so the US Army would escort black students into their high school in Little Rock, Arkansas, after the state’s governor refused to comply with a federal desegregation order. More recently, it was used in 1992 when massive riots broke out in Los Angeles over the acquittal of four white police officers in the beating of Rodney King, a black man. Then-President George Bush sent in active-duty members of the Marines and Army as well as National Guard troops.

Are there any limits on the law?

It was Pearl Harbor–level language. “America’s sovereignty is under attack,” Donald Trump proclaimed on day one of his return to the White House. The president’s cause for alarm? A “National emergency at the southern border,” as the administration labeled it, referring to a frontier that, for all intents and purposes, was comparatively quiet.

The same day, he called on the commanders of the US armed forces to prepare for potential domestic law enforcement. To that end, he asked that plans be drawn up to invoke, if necessary, a nearly 220-year-old “insurrection” law that would give him authority to send federal troops to crack down on the purported southern “invasion. ” Later that week, the new secretary of defense, Pete Hegseth, said in his first remarks at the Pentagon that the military was ready to shift its priorities from possible overseas deployment and engagement to “the defense of the territorial integrity of the United States of America” in compliance with “the Constitution, the laws of our land and the directives of the commander.”

Reminder: shaking free of such ironclad bonds to executive and military authority is why the colonies rebelled against the British in the first place.

And this past weekend, President Trump and Governor Greg Abbott reached a deal to grant the Texas National Guard new authority to make immigration arrests as long as they were alongside immigration officers and border patrol agents. This was, in fact, a “legal action,” but one normally seen only in times of serious crises.

Such declarations and acts seemed chilling, yet specific: Trump’s and Hegseth’s decrees clearly targeted migrants seeking to destabilize the American homeland. Then again, maybe not. Indeed, some have begun to wonder if the president and secretary of defense are preparing for a more all-encompassing contingency: not only an armed bulwark against an already diminishing immigrant influx at the border, but also for a mobilization that could be utilized against political opponents who supposedly threaten the nation’s “territorial integrity”—with troops potentially marching into states and sanctuary cities, even schools and private homes, that resist deportation orders. This is, after all, the playbook of autocrats. Reminder: shaking free of such ironclad bonds to executive and military authority is why the colonies rebelled against the British in the first place.

What might the president be up to? What are the precedents for invoking the Insurrection Act? And what are individual members of the American military doing to anticipate choices they may have to make in the weeks and months ahead?

Trump, it should be noted, flirted with invoking the Insurrection Act during his first administration. That law, which is an amalgamation of statutes enacted between 1792 and 1871, grants the president sole authority to send armed forces into rebellious states, even over the objections of their governments. During the civil unrest that followed the murder of George Floyd, on June 1, 2020, Trump warned, “If a city or state refuses to take the actions that are necessary to defend the life and property of their residents, then I will deploy the United States military and quickly solve the problem for them.” The New York Times noted at the time that Trump planned to announce he was ready to use his powers under the rarely invoked law to override governors and send active-duty troops to states where there were protests. Trump was reportedly dissuaded from such a declaration by senior White House and Pentagon officials.

But that same month, he did send troops into Washington, DC, the one place in the country where he would not face opposition from a governor. That was when peaceful demonstrators were forcefully cleared from Lafayette Square by US Park Police, National Guard members, and law enforcement officers from various federal agencies, including the Secret Service. On that occasion, Secretary of Defense Mark Esper, along with Mark Milley—the chairman of the Joint Chiefs of Staff, dressed in US Army fatigues—walked briefly together with Trump into the square, stopping at St. John’s Church, where the president posed for photographs while holding a Bible.

Shortly thereafter, a chagrined Milley issued an apology for agreeing to take part in such a display. “I should not have been there,” he stated during a commencement address at National Defense University, an educational center for top military and national security leadership in Washington, DC. “My presence in that moment and in that environment created a perception of the military involved in domestic politics. As a commissioned uniformed officer, it was a mistake that I have learned from, and I sincerely hope we all can learn from it.” Milley, now retired and recently granted a preemptive pardon by Joe Biden, still faces Trump’s wrath—including possible demotion in rank—for this and other statements and actions.

The Insurrection Act is murky. Part of the reason is that sending soldiers to do police work is inherently risky, even when seemingly justified. The last time the Insurrection Act was invoked was almost 33 years ago. In May 1992, George H.W. Bush summoned the Marines to help quell the Los Angeles riots that followed the acquittals of four officers charged with assault in the beating of Rodney King. Some 13,500 federal troops, including more than 10,000 from the California National Guard, accompanied the LAPD.

At one point, in the waning days of the unrest, seven marines went along with two local police officers responding to a domestic violence call. What was an ordinary situation for the cops was anything but for the soldiers, according to Joseph Nunn, a lawyer who works with the Liberty and National Security Program of the Brennan Center, an independent think tank. “These Marines now found themselves playing a role for which they had little training: that of civilian law enforcement officer,” he explains in a report on reforming the Insurrection Act. He describes the scene: someone inside the house fired a shotgun through the door. One of the officers shouted, “Cover me.” For the police, that meant: hold your weapons up in a position ready to fire, if necessary. “The Marines,” writes Nunn, “in accordance with their own training, took it as a request for suppressing fire. They riddled the home with more than 200 bullets. Miraculously, no one was killed.”

This is not to say that trained US soldiers are never deployed on American soil. Today, under normal legal precedent, the military is already actively working in support of law enforcement, with some 4,000 federal troops aiding border and Customs agents, though typically without power to arrest offenders. The Pentagon, meanwhile, operates military flights when apprehended immigrants are returned to their home nations. But these activities are different from direct, face-to-face engagement by uniformed military personnel in domestic law enforcement matters. To take that fateful step, Trump would have to invoke the Insurrection Act.

“History makes clear the Insurrection Act is a tool of last resort, not something to be used for routine law enforcement or longstanding policy challenges.”

The first step down this path came on Inauguration Day. Trump’s emergency order set a 90-day deadline for the secretaries of defense and homeland security to have an action plan for obtaining “complete operational control of the southern border, including whether to invoke the Insurrection Act.”

Why would the president need such approval? Because of Congress’s checks and balances on a president’s executive power when it comes to using troops. The Constitution, in various ways, limits military involvement in civilian affairs. But it does not entirely bar federal armed forces from conducting law enforcement actions. Instead, a partial prohibition comes from the Posse Comitatus Act of 1878. In it, Congress expressly forbids federal armed forces from acting as police on the nation’s streets unless such action is authorized by Congress or the Constitution. But there’s one gaping loophole that comes into play only when the president, in a time of national or state emergency, unilaterally invokes the Insurrection Act. According to the Brennan Center: “The Insurrection Act allows the president—with or without the state government’s consent—to use the military to enforce federal law or suppress a rebellion against federal authority in a state.” Even if a state’s government objects, soldiers can, at the president’s behest, march in to stop insurrections and act as police.

In his inauguration speech on January 20. President Donald Trump promised “to launch the largest deportation program of criminals in the history of America.” The president also stated they he would “send troops to the southern border to repel the disastrous invasion of our country. . . [because] as commander in chief I have no higher responsibility than to defend our country from threats and invasions.”

The president knows that absent a massive new authorization and infusion of funds to ICE and CBP, the immigration infrastructure housed inside the Department of Homeland Security (DHS) cannot carry out these plans. Thus, the president’s determination to rely on military support for immigration policy could help make up the difference in financial and human resources needed to carry out the mission. Later on January 20, Trump signed ten executive orders on immigration and border enforcement that repeated some of the rhetoric but also identified legal authorities that would purport to authorize or fund a significant domestic deployment of U.S. military for immigration purposes.

One executive order, Declaring A National Emergency at the Southern Border of the United States, allows the Defense Department to deploy troops to secure the border. President George W. Bush and Barack Obama did much the same thing. More important, the national emergency declaration unlocks funds for further construction of Trump’s border wall, repeating a step he took in 2019. More ominously, the order requires a report from the Secretaries of Defense and Homeland Security within 90 days “regarding additional actions that may be necessary to obtain complete operational control of the southern border, including whether to invoke the Insurrection Act of 1807.”

A second executive order, Protecting the American People Against Invasion, revokes several Biden administration immigration enforcement policies; instructs DHS, its immigration agencies, and the Justice Department to hasten the removal of undocumented persons and the civil and criminal prosecution of immigration law violators; and orders DHS to “construct, operate, control, or use” sufficient removal detention facilities to implement administration immigration policies.

The invasion imagery is, of course, arresting. It conjures Americans’ worst fears, although for most of us the dread springs from apocalyptic Hollywood movies or dramatic tales from science fiction novels. To be sure, the “invasion” label was chosen and repeated for a specific reason having to do with the president’s legal authorities. Regardless of how one characterizes recent trends in migration at our southern border, describing the migration as an “invasion” does not assure the lawfulness of Trump’s determination to utilize the military in immigration enforcement.

The Alien Enemies Act and Potential Role for the Military

The Alien Enemies Act was one of four components of the Alien and Sedition Acts passed by Congress in 1798. The United States was on the brink of war with France and the dominant Federalist Party feared that non-citizens living in the United States would sympathize with France and threaten domestic security during a war. The president can invoke the Alien Enemies Act if Congress has declared war or if the president proclaims an “invasion or predatory incursion … by a foreign nation or government.” Once invoked, the Act authorizes the president to detain and deport any such non-U.S. citizens who were born in the enemy nation, including those lawfully present in the United States, regardless of any reason to suspect that they are dangerous.

The Alien Enemies Act was last used during World War II to intern tens of thousands of non-U.S. citizens of Japanese, German, and Italian descent at military facilities. (The infamous military detention and internment of Japanese-Americans was separately authorized and then upheld by the Supreme Court.) Decades later apologies were issued and reparations paid by Congress for their role in this shameful chapter of wholesale discrimination against people based on their ancestry.

Now, the strongest argument that the Trump administration might attempt is that migration from Mexico or other Latin American countries amounts to an “invasion” or “predatory incursion” at the behest of drug cartels that operate as de facto governments in those regions. On that theory, the Alien Enemies Act permits him to deport Latino immigrants who are undocumented or involved in criminal drug activity indeed, even if they are legally present.

Although the Alien Enemies Act does not authorize military participation in law enforcement, if other laws (reviewed below) permit their use, Trump could enable the military to implement summary detention and deportation of immigrants lawfully in the United States.

When May the Alien Enemies Act be Invoked?

The historical context and structure of the Alien Enemies Act make clear that its terms apply in wartime only. The 1798 Congress sought to address feared armed attacks by a foreign power (France), not individuals fleeing persecution or pursuing economic opportunity. Contemporaneous history and usage of the terms “invasion” and “predatory incursion” confirm the original understanding. James Madison wrote in 1800 that “invasion is an operation of war,” and that while a “predatory incursion” was understood as more circumscribed than an invasion such smaller attacks were known to cause “great destruction.”

Historical examples of the uses and abuses of the Alien Enemies Act confirm that it applies only in wartime and when the invasion or incursion occurs at the behest of a “foreign nation or government.” Drug cartels are hardly de facto governments or foreign nations. The infamous reliance on the Act to intern innocent migrants based on nothing more than their ancestry during World War II was until now the last time the Alien Enemies Act was invoked.

There is no doubt that the Alien Enemies Act confers broad powers on the president. Such expansive authorities are not uncommon for wartime exigencies. However, a reading of the Act to support migrant deportation is at odds with centuries of legislative, presidential, and judicial practice, all of which confirm that the Alien Enemies Act is a wartime authority.

In addition, the few instances where the term “invasion” is found in the Constitution confirm its common usage to refer to intrusions by use of military force. The Constitution empowered Congress to “call[] forth the Militia to … repel Invasions,” but text and historical context underscore that the term anticipated possible hostile incursions by a foreign power, not border crossings by migrants. Similarly, Article IV, Section 4 of the Constitution requires that the “United States shall … protect each [State] against Invasion.” The so-called “Guarantee Clause” was widely understood at the Framing and during ratification to be a bulwark against “foreign hostility” and “bloody” events involving “military talents and experience” and “an appeal to the sword.” Similarly, Article 1, Section 10 prohibits states from engaging in war, “unless actually invaded, or in such imminent danger as will not admit of delay.”

The Importance of Framing Migration as an Invasion

Sometimes rhetoric speaks more forcefully than law. The Trump administration efforts to tar migrants as invaders surely fails to unleash the extraordinarily broad authorities to detain migrants pursuant to the Alien Enemies Act, much less a proper justification to deploy the military to conduct immigration enforcement. Yet the impetus for mass deportations remains, with apparent wide public support, even if in search of legal authority. Framing recent migration as an “invasion” might thus still advance the president’s cause as administration officials begin to implement their enforcement and deportation plans. What follows is a brief sketch of some of the pertinent authorities that prescribe the military role in law enforcement, the pitfalls in their use, and their likelihood of achieving the President’s objectives.

Background Principles

The United States has historically been widely respected for our tradition of entrusting law enforcement to civilians – our federal agents, local and state police, sheriffs, constables. By contrast, our uniformed military fight wars and keep us safe from foreign adversaries and are only episodically needed for domestic assignment. Our traditions are reflected in the Constitution, as noted above, and are explained in part by antipathy to the English Crown and the heavy-handed use of the British military in the colonies. While the Constitution enabled Congress to Call Forth the Militia (today’s National Guard) to “repel Invasions,” the grant of authority was understood to anticipate the possibility of war being brought to the United States.

In 1878 Congress enacted the Posse Comitatus Act (PCA). The PCA created a statutory presumption against military participation in law enforcement, a presumption that could only be overcome by other legal authorities found in statute or the Constitution. Despite the lack of criminal prosecutions for violation of its terms, the PCA has led to a longstanding and pervasive orientation in the U.S. military to steer clear of civilian law enforcement except pursuant to express statutory authorization or to repel a sudden attack on the United States.

A few of those statutory exceptions to the presumptive ban in the PCA loom large in the debates over the military’s involvement in immigration enforcement. It’s also important to note that the PCA applies only to federal armed forces, not to National Guard units unless federalized. State governors control their National Guard units when deployed in their default state status. In addition, the PCA prohibits direct participation in core law enforcement, but indirect support, such as intelligence sharing and providing equipment is allowed (measures that are included in the Emergency Declaration Executive Order). The PCA also does not apply to activities by the military that have a primarily military purpose.

Indeed, if the “invasion” rubric had more than rhetorical force under the Alien Enemies Act, the PCA might not apply. That’s because the executive action could then theoretically become a military operation, not one of law enforcement. It is important to pay attention to one of the executive orders – Clarifying the Military’s Role in Protecting the Territorial Integrity of the United States – which, unlike the others, may be laying the groundwork for that approach.

Military Support for Civilian Law Enforcement Agencies

Several provisions of Title 10 of the U.S. Code authorize federal military assistance to law enforcement agencies, including immigration enforcement. The assistance may include the provision of equipment, personnel for training, expert advice, and military support for counterdrug activities, including military support at the southern border. These authorities have been used across several administrations. Notably none of them authorize direct participation in core law enforcement activities, presumably including search, seizure, arrest, and detention.

In his first term President Trump relied on these authorities to support his actions at the southern border. Because there was no appropriation for these border activities, Trump ordered the Defense Department to utilize its discretion to reprogram funds allocated by Congress for other programs. Although a second Trump administration is again trumpeting the invasion rhetoric to support DoD reprogramming, there are statutory limits that would have to be lifted by Congress to permit significant new spending.

The National Emergencies Act of 1976

The National Emergencies Act (NEA) authorizes the president to declare a national emergency which, once declared, triggers various emergency authorities prescribed in about 150 laws. Many of the statutes enable enhanced authorities for immigration enforcement. In recent years Presidents Trump and Biden relied on the NEA to invoke authorities that permitted call up of armed forces reserve components, including the National Guard, to combat drug trafficking and, in Trump’s first administration to close most cross-border traffic at the southern border. Trump followed suit with a NEA declaration on the first day of his second term. Most notably for Trump’s second term initiatives, one of the emergency authorities allows the Secretary of Defense to undertake military construction projects in a national emergency “that requires the use of armed forces.” Funds may be transferred from military projects that have been canceled or downgraded toward funding, for example, the construction or modification of military bases to serve as immigrant detention facilities. Like the civilian support authorities mentioned above, none of the emergency powers authorize direct participation in core law enforcement activities. In any case, the panoply of emergency powers may well amplify the resources available to the President for immigration enforcement. Moreover, because the NEA does not define “emergency,” any judicial challenge to President Trump’s invocation of the NEA will likely defer to the president’s judgment that an emergency exists. Courts could in any case consider whether the proposed executive actions are authorized by the specific emergency authority invoked. (For more on this topic, I recommend Robert Taylor, A Caution to Pentagon Officials Asked to Obligate “National Emergency” Funds.)

The National Guard and Title 32

In their Title 32 status, state National Guard forces may perform a federal mission – such as immigration enforcement – but remain subject to the governor’s command. Importantly, Guard forces so deployed are not subject to the PCA, such that the soldiers may carry out core law enforcement tasks. During the administrations of Presidents George W. Bush, Obama, Trump, and Biden, Title 32 National Guard forces were deployed at the border. None of their operations included core law enforcement activities but instead involved surveillance, transportation, provision of equipment, and the erection of barriers. That could change in the second Trump administration, but the initial flurry of executive orders authorized only indirect military support to law enforcement.

That said, there are constraints on the uses of the Guard under Title 32. State governors may lawfully refuse the president’s request to deploy troops for a federal mission (more below on federalizing the Guard not upon request, but command). Also, a governor may not send Guard forces into another state without its governor’s consent. In essence, then, Title 32 can support Guard operations only within states that have governors who support Trump’s policies.

The Insurrection Act

The Insurrection Act allows the President to deploy active-duty military and federalized National Guard to enforce federal law or suppress a rebellion against federal authority whenever the president determines that “unlawful obstructions, combinations, or assemblages, or rebellion against the authority of the United States” make it “impracticable” to enforce federal law “by the ordinary course of judicial proceedings.” A lengthy Policy Brief prepared by former and likely future Trump administration lawyers parrots the language of the Act and argues that a migrant “invasion” satisfies the Insurrection Act predicate, making it “impracticable to enforce the laws of the United States.” The Insurrection Act thus allows the President to use the National Guard or units of the regular military following his determination of the impracticability of enforcing the laws with civilian resources. No state officials may stand in their way because the Guard units are operating as federal armed forces. The threshold issue here is whether the claimed predicate of a migrant “invasion” has sufficient legitimacy to it, and as explained above, it does not.

The Insurrection Act has not in the past been relied on to authorize immigration enforcement or border security. However, Trump’s executive order Declaring a National Emergency at the Southern Border of the United States specifically calls for the Secretaries of Defense and Homeland Security to report to the president “regarding additional actions that may be necessary to obtain complete operational control of the southern border, including whether to invoke the Insurrection Act of 1807.” While I have argued in a 2009 law review article that using federal or federalized armed forces to quell domestic violence without a state’s request for federal assistance violates the Guarantee Clause of Article IV of the Constitution, that argument is unlikely to hold sway in the context of the Trump immigration enforcement agenda.

Conclusion

Throughout his first term and his 2024 campaign, Trump himself or through his surrogates painted undocumented migrants as part of an invasion, destined to “poison our blood” as a nation. As rhetoric, “invasion” conjures images of violence and mayhem and strikes fear and dread among many perhaps more impressionable citizens. As underscored in his inaugural address and executive orders issued on January 20, Trump stoked those same flames. Now that he is president again, he has considerable though not unlimited authority to follow through on his promises to seal the southern border, reduce the influx of migrants, and remove undocumented immigrants from within the country. To the extent he relies on the U.S. military to help carry out his more expansive aims, the president will be testing the longstanding orientation of our military to be uninvolved in domestic law enforcement. There are legal guardrails that have long served to prevent civilians from misusing military power. Let’s hope that those guardrails remain firmly in place.

Editor’s note: This piece is part of the Collection: Just Security’s Coverage of the Trump Administration’s Executive Actions

IMAGE: A US Army soldier monitors the US-Mexico border in Eagle Pass, Texas, on January 24, 2025. (Photo by Charly Triballeau/AFP via Getty Images)

FEATURED IMAGE: A US Army soldier monitors the US-Mexico border in Eagle Pass, Texas, on January 24, 2025. US President Donald Trump ordered 1,500 more active military personnel to the border with Mexico as part of a flurry of steps to tackle immigration, his spokeswoman said on January 22. Border security is a key priority for the president, who declared a national emergency at the US frontier with Mexico on his first day in office, and the additional personnel will bring the total number of active-duty troops deployed there to around 4,000. (Photo by CHARLY TRIBALLEAU / AFP) (Photo by CHARLY TRIBALLEAU/AFP via Getty Images)