While trying to define Democratic rival Joe Biden as an avatar of lawless anarchists, President Trump has warned about rioters in the streets of liberal American cities. He has fanned fears of low-income minorities invading the suburbs.

And this week, he offered a new alert: “Thugs wearing dark uniforms,” he told Fox News host Laura Ingraham, had crowded en masse onto a plane to fly to Washington and wreak havoc at the Republican National Convention last week.

“A lot of people were on the plane to do big damage,” Trump declared in a prime-time interview Monday.

When asked to elaborate Tuesday, the president told reporters that a well-known figure, who was also aboard, had informed him. “The entire plane was filled up with the looters, the anarchists, the rioters, people that obviously were looking for trouble.”

Lacking details, the fantastical tale took on the wild, conspiratorial tone of a subversive Reddit subchannel or a foreign government’s disinformation campaign. That it was coming from Trump on a popular cable news show highlighted how his long-standing willingness to promote and disseminate conspiracy theories has become, in his view, central to a reelection effort that has foundered during the coronavirus pandemic.

“What does that mean? That sounds like a conspiracy theory,” Ingraham remarkedafter Trump stated that people in “dark shadows” were controlling Biden’s agenda.

In recent months, Trump has touted the effects of sunlight, bleach and hydroxychloroquine, an anti-malaria drug, as potentially beneficial to protect against the coronavirus — despite warnings from medical authorities that such practices are ineffective or even dangerous. He has promoted a false conspiracy called “Obamagate,” which holds that Biden and other Obama administration figures tried to “spy” on his 2016 campaign….