Trump did not explain why Johnson's deal with Brussels would hinder one with Washington. It apparently has to do with technical provisions known as geographical indications. Trade experts split on how much of a hurdle they pose, but the details mattered less than the theatrics.
As Johnson and the Labor leader, Jeremy Corbyn, took to the campaign trail to begin framing their messages, Trump stole the limelight by giving a freewheeling interview to Farage, an insurgent figure who leads a fringe party that could inflict damage on both Labour and Johnson's Conservatives.
"I'd like to see you and Boris get together because you would have some real numbers," Trump said to Farage, who has proposed aligning with the Conservatives but has been rebuffed by Johnson.
"I have enough to do over here without having to worry about the psychology of two brilliant people over there, frankly," Trump added. "I wish you two guys could get together. I think it would be a great thing."
Trump saved most of his vitriol for Corbyn, who has painted the president as a predatory rival eager to use trade negotiations to gain access for US companies to Britain's National Health Service.
"He'd be so bad; he'd take you in such a bad way," Trump said, "He'd take you into such bad places." Noting that he had never met Corbyn, he added, "I'm sure he's a lovely man, but he's of a different persuasion."
Corbyn promptly fired back on Twitter, saying that Trump "is trying to interfere in Britain's election to get his friend Boris Johnson elected." He added that Trump has long had designs on the National Health Service and "knows if Labour wins, US corporations won't get their hands on it."
Trump was generous to Johnson, praising his efforts to take Britain out of the E.U. as quickly as possible. "He's willing to do what no one else would do," the president said.
But the only clear winner from Trump's intervention was Farage, whose Brexit party has been casting around for ways to influence the election.
Johnson had hoped to neutralise the party by negotiating Britain's departure from the EU by October 31. But he failed to win approval in Parliament for his deal with Brussels and was forced to ask European leaders for a three-month extension.
Johnson plans to campaign on that deal as the swiftest route to Brexit. But Farage has called on the prime minister to drop the deal and leave the EU with what he calls a "clean break." The Brexit Party is debating how many candidates to field and how aggressively to go after Conservative-held seats.
Written by: Mark Landler
Photographs by: Doug Mills
© 2019 THE NEW YORK TIMES