At the start of their careers, Sens. Kirsten Gillibrand, D-N.Y., and Joni Ernst, R-Iowa, had very little in common. Gillibrand was born in upstate New York and worked for a Manhattan-based law firm. Ernst joined the reserves after graduating from Iowa State University and rose to become a lieutenant colonel in the Iowa Army National Guard.

But as stories surrounding sexual harassment and assault in the military multiplied, and how the military conducted investigations (or didn’t) came to light, the two senators found a common cause. That cause and friendship became stronger when they traveled together to Afghanistan in 2019, as The 19th and others have reported.

Anecdotes abound about how trips taken by congressional delegations (called CODELs) have led to social relationships, and then to bipartisan legislative collaborations. Two House members once hashed out some AmeriCorps funding questions on a return flight from Europe. The primary drivers of the major $1.2 trillion infrastructure bill that became law in 2021 were Rob Portman and Kyrsten Sinema, senators on opposite sides of the aisle. The pair first bonded on a civil rights trip to Selma, Ala., to walk together over the Edmund Pettus Bridge.

“Trust,” Portman said in an interview with The New York Times, when asked why the partnership worked. “It was because we saw an opportunity to do something good for the country, making lemonade out of lemons.”

Now, two academic researchers have developed quantitative metrics that show how these trips lead to bipartisan bills. Professors James M. Curry of the University of Utah and Jason M. Roberts of the University of North Carolina at Chapel Hill conducted a study of the publicly available reports that committees and members of Congress must file related to their trips. They examined 372 reports from 1994 to 2020 and then followed up with 21 in-depth interviews with senior congressional staff.

The metric of bipartisan collaboration used in the study was simple: Was one member an original co-sponsor of a bill sponsored by a travel mate of the opposite party?

“Original co-sponsorship is almost like co-authoring the bill together,” Roberts said in a recent interview. “It’s a sign they are truly collaborating in a one-on-one way.”

The researchers found a direct correlation between members who traveled together and increased original co-sponsorships. In comparison to a non-traveling colleague, a frequent traveler might have an original bipartisan co-sponsorship rate that is 5 percent higher.

“Every single interview participant—100%—noted travel was the single best way to develop relationships in the contemporary Congress,” the authors noted in a journal article published in Legislative Studies Quarterly in 2023.

“Both staff and members spend time together in close quarters, often not great conditions,” said one staffer interviewed for the study. “It’s like a trip with an extended family. I think they make a big difference. They share these moments together.”

The media and some outside groups often rail against these trips, portraying them as taxpayer-funded vacations. And it’s true that some members of Congress get caught engaged in stupid antics, like the member who went skinny-dipping in the Sea of Galilee on a CODEL to Israel. However, the reality is often quite different.

Most schedules for these trips are jam-packed, with meetings starting at breakfast and ending after dinner. Sure, they include fascinating tours of foreign legislatures and thought-provoking meetings with leaders of other nations. They also include mundane briefings and very long hours. Additionally, they include time for lawmakers to get to know one another.

“Overseas travel is a healthy thing for Congress, as it helps Congress see what’s going on in countries around the world. It also helps build relationships and collaboration across the aisle,” Roberts said.

“When you’re out of your element in a group, the dynamics change greatly,” said a staffer interviewed for the study. “There’s a lot more opportunity through that shared experience to break down political barriers.”

And that shared experience leads to relationship-building and trust. “Our findings strongly suggest the importance of interpersonal relationships in promoting legislative collaboration, including across party lines,” the researchers wrote.

The Gillibrand-Ernst partnership paid off. Their proposal to overhaul the investigation and prosecution of sexual assault cases in the U.S. military was passed into law as part of the 2023 defense policy bill, and the Pentagon implemented a new system soon thereafter.

Their travel together wasn’t the only factor in forging their partnership. (According to The 19th, apparently Gillibrand makes an awesome meatloaf, which she served to Ernst during family dinners at her D.C. residence). Yet the research and the stories can’t be denied: Congressional travel can build bipartisan relationships between members of Congress, strengthening trust and translating to constructive legislative accomplishments.

Bradford Fitch is a former Capitol Hill staffer, former CEO of the Congressional Management Foundation and author of “Citizen’s Handbook for Influencing Elected Officials.”