There is no cause on the American right quite like the quest to save children from sex abuse.

The harming of children is at the center of Pizzagate, the wholly fake theory that began circulating around the 2016 election that Hillary Clinton was running a child sex-trafficking ring out of the basement of a Washington, D.C., pizza parlor. It’s the ultimate sin in the tales spun by QAnon followers, who believe that millions of children are going missing, their bodies harvested for a drug enjoyed by elites.

The obsession can be found closer to the mainstream, too. Conservative activists have stoked fears that transgender adults are “grooming” children for abuse. In the summer of 2023, the movie “The Sound of Freedom,” a thriller about a swaggering federal agent who rescues children from sex trafficking, was an unexpected blockbuster, powered by loyal conservative fans.

And now the great MAGA meltdown over Jeffrey Epstein.

Unlike QAnon or Pizzagate, Mr. Epstein’s abuse of minors has been proved in a court of law. Theories about his connections to powerful figures and the records of his crimes have been fodder for right-wing media for years. Now, Mr. Trump’s insistence that the whole thing is a “hoax” is being met with disbelieving anger from the MAGA base. Polling shows that the issue is the rare case where Trump supporters break from the president.