Egged on by his most ardent followers, Donald Trump’s public-influence campaign against the F.B.I. has dogged each new stop of Robert Mueller’s investigation. From casting doubt on key players in the bureau to waging a proxy war to discredit Mueller himself, Trump and his allies have sought to weaponize public opinion, even as doing so may further ensnare them in Mueller’s obstruction-of-justice case. This week, the president and his allies have seized on a new talking point to justify their animosity toward the bureau: “Wow, word seems to be coming out that the Obama F.B.I. ‘SPIED ON THE TRUMP CAMPAIGN WITH AN EMBEDDED INFORMANT,’” Trump tweeted on Thursday morning. “If so, this is bigger than Watergate!”

The allegation, which at this point is largely conjecture, emerged out of a battle between Republican Congressman Devin Nunes and the top brass at the Justice Department over the release of documents detailing the origins of the investigation into the Trump campaign. Earlier this month, F.B.I. and law-enforcement officials informed the White House that a request from the California lawmaker could endanger a top-secret intelligence source who provided information in the early stages of the probe, according to The Washington Post. (“What we’re trying to figure out are what methods the F.B.I. and D.O.J. used to investigate and open a counter-intelligence investigation into the Trump campaign,” Nunes told the paper.) Nunes’s worst fears were seemingly confirmed by a New York Times report on Wednesday, which noted that “at least one” government informant met “several times” with Carter Page and George Papadopoulos at the outset of the investigation.

Trump’s loyal base has used the tantalizing claim of a malicious embedded spy to argue for a kamikaze strike against the bureau. “The prior government did it, but the present government, for some reason I can’t figure out, is covering it up,” Rudy Giuliani said in an interview with the Post on Thursday. He added that the president believes classified documents pertaining to the origin of the probe should be released. “It’s ridiculous,” he said. “I don’t know why the current attorney general and the current director of the F.B.I. want to protect a bunch of renegades that might amount to 20 people at most within the F.B.I.” “It looks like the Trump campaign in fact may have been surveilled,” White House adviser Kellyanne Conway said Thursday on Fox News. “It looks like there was an informant there. As the president likes to say, we’ll see what happens.”

Trump’s congressional allies, too, have shared their suspicions directly with the president. According to “multiple people” familiar with their chats, Rep. Mark Meadows, chairman of the House Freedom Caucus, has been calling Trump three or more times a week to “[communicate] concerns that the Justice Department is hiding worrisome information about the elements of the probe.” Nunes has publicly validated the president’s concerns, telling the Post, “If you are paying somebody to come talk to my campaign or brush up against my campaign, whatever you call it, I’d be furious.”

Chief of Staff John Kelly has reportedly complained that Nunes’s and Meadows’s encouragements are “not always helpful,” per the Post, but they certainly seem to have taken root in Trump’s psyche; he doubled down on the topic in a Friday Twitter rant. “Apparently the D.O.J. put a Spy in the Trump Campaign,” he wrote, quoting Fox Business Network host David Asman. ”This has never been done before and by any means necessary, they are out to frame Donald Trump for crimes he didn’t commit.” Within hours, he was back at it. “Reports are there was indeed at least one F.B.I. representative implanted, for political purposes, into my campaign for president,” he tweeted. “If true - all time biggest political scandal!”