Ordinarily, they go after foreign spies and federal felons. Now, the FBI, the Department of Justice, and the nation’s counterintelligence executive will use their finite resources to go to war with people who leak classified information to reporters. The bureau has a new team dedicated solely to this work, and the DOJ’s powerful National Security Division has been ordered to prioritize the leak hunt.

But Attorney General Jeff Sessions—and his allies on Capitol Hill, and his boss at 1600 Pennsylvania Avenue—might want to take a deep breath before plunging too deep into this crusade. If history is any guide, they might not like how this leak hunt ends up.

While some White House allies railed on Friday against a “fishing expedition” into Trump-Russia ties, Sessions put reporters on notice: Journalists may face more pressure than ever to reveal their sources. Sessions announced that the DOJ is reconsidering its current approach to subpoenaing reporters.

The Justice Department currently has nearly three times as many active leak investigations as the number pending at the end of the Obama administration, he added.

Sessions also claimed that some news stories based on leaked classified information put members of the American military at risk. His top deputy, Rod Rosenstein, declined to tell reporters afterward which stories they believe put people in danger.

“We are taking a stand,” Sessions said. “This culture of leaking must stop.”

Ron Hosko, former deputy director of the FBI, said these changes could result in prosecution of members of Congress and Hill staffers. In the past, he said the FBI identified members of Congress who leaked classified information, who the Justice Department then declined to prosecute. Agents were often frustrated by this, Hosko added. Given the attorney general’s announcement, he said, members of Congress and Hill staffers may be more likely to face prosecution.

“Let’s face it: Capitol Hill leaks like a sieve,” Hosko said.

“I think that Sessions is trying to change the calculus,” he added. “He’s issuing a threat to those who leak and he is, perhaps, telling his own investigators and prosecutors to be more aggressive in finding it and in charging it.”

The announcement drew immediate condemnation from First Amendment advocates.

“The guidelines in place carefully balance the interests of both law enforcement and the news media,” tweeted the Reporters Committee for Freedom of the Press. “We strongly oppose DOJ plan to revisit.”

In 2015, advocates worked with Justice Department officials to put together regulations on how the department handles leak investigations that involve reporters. But some argued those regulations should have been made the law so a future administration wouldn’t be able to change them. But that didn’t happen, and now those protections may be weakened.

“Our warning was that the next president could simply undo it,” said Kathleen McClellan, deputy director of the Whistleblower and Source Protection Program. “And that’s exactly what’s happening.”

Jesselyn Radack, who heads that program, said the attorney general’s move to crack down on leaks means the government has broader problems.

“It’s a sign of an unhealthy government that they’re going to create an entire FBI unit to be looking at internal leaks,” she said. “It says to me it’s more about chilling dissent and chilling info that the government doesn’t want out there rather than anything related to a legitimate law enforcement need.”

It’s unclear how the Justice Department may change its internal regulation protecting reporters. But the fact that they’re thinking about it has generated significant concern.

“The attorney general’s intent to revisit the guidelines is deeply troubling as is the frame he put around it today – that reporters are putting lives at risk,” said Bruce Brown, executive director of the Reporters Committee for Freedom of the Press. “Journalists and news organizations have a long history of handling this information in a responsible way, working with government officials to evaluate potential harms, and taking steps to mitigate any damage when there is an overwhelming public interest in revealing it.”

Some conservatives – including Tea Party leaders who have spent years publicly praising the Constitution – hailed Sessions’ crackdown.

“Today’s announcement of an investigation into damaging leaks that have harmed our national security is just the latest example of how A.G. Sessions is proving to be an effective Attorney General,” said Tea Party Patriots president Jenny Beth Martin.

Tony Perkins, a top Trump ally who runs the Christian conservative Family Research Council, also praised the move.

“Jeff Sessions is already proving to be a very effective attorney general of the United States because he enforces the law as written, rather than how some would like it to be,” he said in a statement.

Perkins may want to take a bit more of a wait-and-see approach. These leak investigations have a habit of taking some rather odd turns. President Nixon’s anti-leak team—the so-called “plumbers”—eventually helped bring down his presidency.

Or look at the last war on leakers—the one waged by the Obama administration. Furious over the spilling of classified details about the cyber espionage campaign against Iran, counterterrorism operations in Yemen, and the mission to kill Osama bin Laden, the Obama-era DOJ fanned out.

The biggest catch: one of the president’s most trusted advisors, General James “Hoss” Cartwright, the man known as “Obama’s favorite general.”