President Trump pushed a baseless and bizarre conspiracy theory on Monday that a plane “almost completely loaded with thugs” was sent to disrupt the Republican National Convention, a claim that appears almost identical to a rumor that traveled across Facebook three months ago.

Trump made the claim in an interview with Fox News host Laura Ingraham, alleging without evidence that “we had somebody get on a plane from a certain city this weekend, and in the plane it was almost completely loaded with thugs, wearing these dark uniforms, black uniforms, with gear and this and that.”

While the president would not divulge more details, he assured Ingraham that the incident is “under investigation right now.”

There is no evidence of such a flight. When Ingraham asked Trump to say more, the president replied, “I’ll tell you sometime.” The unidentified black-clad “thugs,” the president said, were headed to Washington D.C., to disrupt the RNC.

NBC News’ Ben Collins later reported that the rumor lines up with a viral Facebook post from June 1, which falsely claimed to have observed a similar sinister contingent on board a flight from Seattle to Boise, Idaho: “At least a dozen males got off the plane in Boise from Seattle, dressed head to toe in black.”

That post — apparently from a man from Emmett, Idaho — advised Boise residents: “Be ready for attacks downtown and residential areas,” claiming that one group member had “a tattoo that said Antifa America on his arm.”

Collins reports that the Facebook post had been shared more than 3,000 times, and other pages from the area “added their own spin,” including the state branch of right-wing militia group the 3 Percenters.

One such post, Collins writes, alleged that the Payette County Sheriff’s Office had confirmed that “Antifa has sent a plane load of their people.” This wasn’t true, and the post spread so widely that the actual Payette County Sheriff’s Office felt compelled to release a statement clarifying that the rumor was “false information.”

Earlier in the Ingraham interview, Trump claimed vaguely that there are “people that are in the dark shadows,” and that Democratic nominee Joe Biden was being controlled by “people that you haven’t heard of.”

Ingraham pointed out that this sounded like a conspiracy theory.

“They’re people that are on the streets. They’re people that are controlling the streets,” Trump explained.

While Trump’s theories perplexed many observers beyond Ingraham, they echoed months of steady rhetoric from Trump confidant and former LifeLock spokesperson Rudy Giuliani, who himself told Ingraham in an interview this June that the Black Lives Matter social justice movement “wants to come and take your house away from you.”

Ingraham had asked Giuliani about the “planned and well-funded attack going on” in Washington, alluding to a small group effort to topple a statue of former President Andrew Jackson on government property.

“Well, over this weekend it should be quite plain to every American who can see through the propaganda that antifa, Black Lives Matter, the communists and their allies are executing a plan they wrote about four or five years ago,” Giuliani replied.

“Just go back and read what they wrote in the manifestos that they wrote, including Black Lives Matter,” he continued.

Giuliani rattled off a litany of institutions that antifa, Black Lives Matter, the communists and their allies supposedly want to “destroy,” including the United States government itself, the police and prisons.

“They want to internationalize our government,” he claimed, without explanation. “They want to do away with our system of courts, and they want to take your property away and give it to other people.”

 “This is an anarchist — organized anarchists, supported with a lot of money,” Giuliani said, without offering any evidence or supporting the claim further.

“We had outbreaks in about 30 cities over the weekend [in June],” Giuliani added. “There were well over 100 people wounded with guns and 25 Americans killed over the weekend. That didn’t happen accidentally, Laura,” he claimed. “That’s part of a plan — and we better wake up to it, and we better stop being silly.”

“People who say they are favorable to Black Lives Matter — Black Lives Matter wants to come and take your house away from you,” Giuliani added. “They want to take your property away from you. They want to let criminals out of prison — all criminals out of prison,” Giuliani continued.

“They are anarchists, and they are anti-American,” he concluded.

Earlier that month, conservative media personality Piers Morgan had called the former mayor “completely barking mad” in a discussion about race relations. Not long after Giuliani’s string of cable news rants, Trump first introduced the idea that Democrats want to “destroy the suburbs” as a campaign talking point in a speech from the south lawn of the White House.

“Joe Biden and his bosses from the radical left want to significantly multiply what they’re doing now, and what will be the end result is you will totally destroy the beautiful suburbs,” Trump said at the time. “Suburbia will be no longer as we know it.”

Around the same time, Trump appeared to echo another misleading point that Giuliani had recently espoused on cable news about the rates at which police kill white people versus Black people.

Collins, who covers disinformation and social media for NBC News, has reported before on false social media rumors about roving gangs of antifa supporters, which have had real-world impact.

In June, for instance, fake Facebook rumors inspired people to take over central squares in several American towns to defend them against busloads of imaginary antifa invaders. A week after the original “thugs on a plane” rumor went viral in Idaho, a group of armed men showed up in Missoula, Montana, to observe protests in the town, concerned that planeloads of antifa might descending to wreak havoc on that heartland city.