The FBI Is Investigating Whether President Trump Broke the Espionage Act. Here’s What to Know About the Law

When FBI agents seized 11 sets of top-secret and sensitive documents from former President Trump‘s Florida residence Mar-a-Lago, per a search warrant revealed on Friday, it was an unprecedented moment—but one that could be traced back to a law that’s more than a century old.

The warrant shows that the agency is investigating whether Trump violated the Espionage Act of 1917. Senator Rand Paul, a Kentucky Republican, was quick to call for a repeal of the law, dismissing it as outdated. “The espionage act was abused from the beginning to jail dissenters of WWI,” he tweeted. “It is long past time to repeal this egregious affront to the 1st Amendment.”

But while the law—which was designed to prevent the unlawful retention of information about national defense, which a foreign enemy could use to harm the U.S.—passed during World War I, to crack down on people who criticized the war, NPR reports that lawmakers repealed the strict censorship sections of the law in 1920.

And perhaps it’s not entirely surprising that the law would find a new spotlight today, at another moment rife with fears about a betrayal of the U.S.

Read more: Analysts Warn Violent Rhetoric After FBI Mar-a-Lago Search Is a Preview of What’s to Come

As TIME has previously reported, World War I amplified xenophobia and fears that immigrants would inspire an uprising akin to the Russian Revolution, which started in 1917. In 1918, Eugene V. Debs, Socialist Party presidential candidate, was arrested and sentenced under the Espionage Act to 10 years in prison after being accused of delivering a speech designed to cause “disloyalty” and “insubordination.”

“There was a crackdown on dissent, and simple criticism of the government was enough to send you to jail,” Christopher M. Finan, author of From the Palmer Raids to the Patriot Act: A History of the Fight for Free Speech in America, told TIME.

Following the war, a combination of job losses and high inflation only exacerbated those fears, and employers were on heightened alert for communist infiltration when more than 3,600 workers went on strike in 1919.

Prosecutions under the Espionage Act have been relatively rare. Notable uses of the law include the 1957 arrest of Colonel John C. Nickerson Jr., “the first American to be prosecuted for leaking top-secret national security information to the press,” according to historian Sam Lebovic. As Lebovic detailed in an article for Politico, Nickerson supervised a missile program and agents discovered unsecured classified documents in his Huntsville, Ala., home. In the 1970s, Daniel Ellsberg faced charges under the Espionage Act for leaking the Pentagon Papers, but a judge dismissed the charges.

In 2017, Wikileaks document dumps sparked conversation about the Espionage Act, and the Congressional Research Service outlined the main uses of the law throughout American history, stating, “Historically, the Espionage Act and other relevant statutes have been used almost exclusively to prosecute (1) individuals with access to classified information (and a corresponding obligation to protect it) who make it available to foreign agents, and (2) foreign agents who obtain classified information unlawfully while present in the United States.”

The Obama Administration used the Espionage Act more than any other presidential administration, with federal criminal charges filed against eight whistleblowers, including Chelsea Manning and Edward Snowden.

The Trump investigation would represent the first time that someone who served as President has been the subject of an Espionage Act probe.