The White House said the two leaders pledged to negotiate “a robust bilateral free trade agreement once the United Kingdom leaves the European Union.” Downing Street said nothing about a deal, noting instead that Mr. Johnson urged Mr. Trump to lift American tariffs on Scotch whisky.

Such divergent accounts of a leader-to-leader call are not unheard-of, but the timing of this one, on the eve of Britain’s general election campaign, was telling. It shows just how much of a liability Mr. Trump has become for Mr. Johnson. Once, the prime minister talked up the benefits of having a close friend in the White House; now he is distancing himself from a figure who is radioactive to many Britons…

What makes Mr. Trump so dangerous for Mr. Johnson is his unpredictability — and his penchant for butting in. He called in to a London radio show last week with unsolicited advice for Mr. Johnson’s campaign, and Mr. Trump is expected in London for a meeting of NATO leaders in early December, just a few days before Britons go to the polls.