Boris Johnson’s time as prime minister has at last reached its denouement.

On Tuesday evening, two of the biggest players in his government — the chancellor of the Exchequer, Rishi Sunak, and the health secretary, Sajid Javid — resigned within moments of each other, swiftly trailed by lawmakers, junior ministers and parliamentary assistants.

On Wednesday, things got worse: A cascade of resignations culminated in an extraordinary encounter at 10 Downing Street, the prime minister’s official residence. A host of cabinet members assembled, telling Mr Johnson to step down. He refused, but by Thursday morning he had agreed to resign as Conservative leader. He plans to stay on as prime minister until the autumn, though it’s unclear that he’ll be able to.

The immediate cause of the prime minister’s downfall was another scandal. In recent days, it emerged that Mr Johnson had appointed a lawmaker named Chris Pincher to a job overseeing discipline and welfare in the Conservative Party, despite allegations of sexual misconduct against him. The prime minister first tried to claim that he had not known about the allegations. To much outrage, it was then demonstrated that he had.

The scandal, while undeniably bad, is hardly the worst offence Mr Johnson has committed. (The contenders for that distinction are too numerous to mention.) And yet it proved the undoing of a man who for months had thwarted every expectation that he would be removed from office, a man whose bluster and bullishness seemed to transcend every rule of political practice. In this fevered atmosphere, there are many questions swirling around British politics. One of the most pertinent is: Why now?

Of course, the answer in part is that Mr Sunak and Mr Javid, alive to the deep discontent in the party, have been waiting for an opportune moment to bring down the prime minister. But what made this moment the right one?

It seems odd, but what may in fact have brought down Mr Johnson was not a scandal but an apology. On Tuesday, he broke with the habit of a political lifetime and admitted to personal wrongdoing in the Pincher appointment. “It was a mistake,” he said, “and I apologise for it.” Minutes later, the resignations began.

In a tenure marked by scandal and controversy, Mr Johnson has occasionally expressed regret or halfheartedly suggested that things would change. But he made a point of never fully apologising. It was, alongside his boisterous humour and unflappable demeanour, a cornerstone of his conduct and style. Now, as the country awaits his removal within days, he might reflect that of all his miscalculations, the most fatal one was to say he was sorry.

Mr Johnson should have known better. In January, pressed to respond to mounting evidence he had broken pandemic restrictions, he lost his usual exuberance. “I deeply and bitterly regret that happened,” he said in a television interview, looking at his feet. The backlash was instant.

Conservative lawmakers, until then relatively sanguine about the emerging details about partying at Downing Street, came forward to say they had submitted letters of no confidence. One left to join another party. Commentators predicted his imminent removal. The drama calmed down only when, the next day, Mr Johnson returned to his unrepentant style, waving away objections and behaving as though nothing was wrong.

In the weeks and months that followed — during which an independent inquiry found government officials to have violated Covid restrictions and the prime minister’s approval ratings nose-dived — it was only when Mr Johnson was fined by the police for attending an illegal party that he came close to apologising. But there too it was of the partial, self-excusing kind. And even when a no-confidence vote was called, he refused to strike an emollient tone.

It worked, just: Mr Johnson squeaked home, with two-fifths of his party voting against him. That seemed to be a stalemate, likely to stretch through the summer. Then came the events of the past week.

It’s worth reflecting on why an apology should seem to have changed the calculus so much. In truth, the decision to punish moral transgressions is often less straightforward than we like to admit. Scandals tend to break not at the point people “find out” about bad behaviour — stories of Mr Pincher’s misconduct had long been circling in Westminster, for example — but when they think a majority of others judge it to be wrong. People, after all, rarely make ethical judgments in a vacuum.

In politics, where support can be counted to the number, that perhaps holds especially true. Offered in the hope of mitigating damage, apologies often instead open the floodgates. By confirming you did something wrong, you give your accusers permission to pursue retribution. It puts beyond doubt that they are correct to judge you. That’s not to say politicians are wrong to apologise when they have made a mistake, of course. It’s just that, in politics, it tends not to go well.

This is not a new phenomenon even if, in these brazen times, the political cost of apology seems to have risen. Richard Nixon, for example, sealed his tarnished reputation when he apologised for his actions. The political career of a British deputy prime minister, Nick Clegg, never recovered after he apologised for breaking an election pledge. And the apologies offered by Al Franken when he was accused of sexual harassment are widely regarded to have weakened his position.

Mr Johnson seemed, more than any of his predecessors, to grasp this fact. His knack for not apologising was remarkable. His breezy denials induced a sort of cognitive dissonance in the minds of those accusing him — Was there some fact they had missed? Were they going mad? Was he? — and permitted supporters to make their own denials, too. In recent months, it produced a sort of moral vacuum in Britain’s government, in which nobody seemed to have the power to hold the prime minister to account.

No longer. Mr Johnson’s grasp on power is effectively over. It’s presumably no consolation that he has no one to blame but himself.

This article has been updated to reflect news developments.

This article originally appeared in The New York Times.

Martha Gill is a political journalist and a columnist for The Evening Standard and The New Statesman.

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