But as optimistic as the Chequers plan looks to outsiders, it seemed desperately unsatisfactory to pro-Brexit politicians. They envisioned a Britain free to negotiate free-trade agreements with fellow-English-speaking countries: the United States, Canada, and Australia. They had promised to claw back billions of pounds in payments to the European Union and redirect them to the U.K. health system. They insisted that British trade agreements should be enforceable only by British courts. The Chequers plan implicitly surrendered these high hopes.

And so, in protest, two ministers quit: first David Davis, the minister in charge of the negotiations, then the ferociously ambitious foreign secretary, Boris Johnson, determined as always to position himself as the most Euroskeptical politician in Britain.

Had Brexit lost, Johnson would today occupy a comfortable position in British politics. He would be the acknowledged leader of the die-hard Euroskeptic faction within the Conservative party. The wittiest man in politics, the best debater in the House of Commons, he would be free to scheme and plot without having to worry about the tedious, technical difficulties of trade negotiations.

Unfortunately for him, his side won the referendum—and his reputation has been in free-fall ever since. Only 50 percent of Conservative Party members regard Johnson as competent, by far the lowest ranking of any of the top five candidates to succeed May. (Among non-Conservatives, Johnson stands even lower. The New Statesman last year quoted a former British ambassador who called Johnson “the least deserving and least qualified foreign secretary of modern times, who has successfully lived down to all expectations.”) His resignation from the Cabinet is a last bid to regain the factional leadership he has botched.

While Johnson lacks interest in the dull details of policy, he is Britain’s leading expert in the dark arts of sabotaging potential rivals. He seems on the verge of doing it again. His resignation has up-ended the May government and could yet collapse it. But those ruthless tactics are not joined to much concern for political outcomes. The Conservative government is teetering even as Britain moves ever closer to being cast out of the EU without any deal at all, leaving unsettled such terrible problems as the Irish border—putting at risk the hard-won Irish peace of the 1990s.

Right now, people and goods cross between Northern Ireland and the Irish Republic as easily as between Maryland and Virginia. (One video shows a single automobile crossing the border four times in 10 minutes of driving, all on the same road.)

If the Irish border remains open post-Brexit, any resident of the EU could fly to Dublin, take a bus to Belfast, and then fly to London—all without showing a passport.* That would make a mockery of the Brexit promise to restrain immigration.