LONDON — “I am increasingly admiring of Donald Trump. I have become more and more convinced that there is method in his madness.” These comments, subsequently leaked, were made last month by Boris Johnson, who was then Britain’s foreign secretary. Never one to discount praise, Mr. Trump reportedly expressed an interest in meeting his “friend” Mr. Johnson during his visit to London this week, noting that Mr. Johnson has been “very, very nice to me, very supportive.”

When Mr. Johnson offered those remarks praising the American president, he was discussing the topic that shapes everything in British politics right now: Brexit. The dilemma that is pulling Prime Minister Theresa May’s government apart, and may yet topple her, is whether Britain opts for a “soft” Brexit, in which it leaves the European Union but retains many of its rules, or a “hard” Brexit, which throws caution to the wind and releases Britain to start all its trading negotiations afresh. In Mr. Johnson’s view, it seems, Mr. Trump would have no hesitation in choosing the latter. One thing the two men share is a recklessness that looks like courage in the eyes of their supporters, but which also sabotages the work of policymaking and diplomacy.

Mrs. May’s most recent attempt to escape the “hard” versus “soft” dilemma involves establishing a “common rule book” shared by London and Brussels. This looks far too “soft” for the liking of fervent Euroskeptics in her party. Within 48 hours of the plan’s being revealed, Mr. Johnson had resigned. Before him, so had David Davis, another prominent Brexiteer in Mrs. May’s cabinet who had been put in charge of negotiating with the European Union. In characteristically florid terms, Mr. Johnson’s resignation letter expressed fears that “we are headed for the status of a colony.”

Just to further destabilize an already fragile political situation, Mr. Trump's visit has been accompanied by an incendiary interview with The Sun. Confirming Mr. Johnson's assessment, while escalating the mutual admiration between the two men, Mr. Trump declared that Mrs. May's plan would “kill” any future trade deal between Britain and the United States, and that Mr. Johnson would “make a great Prime Minister.” On the lengthy efforts of Mrs. May's government to arrive at a compromise with Brussels, Mr. Trump scoffed that “deals that take too long are never good ones.”