Justin Trudeau waited until all the options were gone, painting the party and country into a corner

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A decade ago, Justin Trudeau titled his ghostwritten autobiography Common Ground. On Monday, he was walking away from scorched earth.

He will roam around the Prime Minister’s Office for two months, give or take, a lame duck fighting a U.S. tariff threat. He told reporters he is a fighter, implying he had wanted to fight on, but divisions in his party meant he is no longer the best choice. “Removing me from the equation,” he suggested, should reduce polarization in Canada’s politics.

But he left that all too late. Mr. Trudeau couldn’t see the scorched earth around him till the flames were up around his nose.

U.S. president-elect Donald Trump arrives at the White House in two weeks with the threat of economy-roiling tariffs. Parliament hasn’t approved the funding the government needs after April 1. The Liberal government is set to fall right after Parliament comes back on March 24.

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By the time Mr. Trudeau made his announcement, his party and the country were painted into a corner. The Liberal Party must rush a leadership race to pick a new prime minister who will face an immediate election campaign. Parliament had to be prorogued so the government doesn’t fall in the meantime. A custodian PM has to negotiate with Mr. Trump.

Rarely has an outgoing prime minister left his successor so few options. Even Brian Mulroney, who quit in the fifth year of his mandate in 1993, announced his departure from his party eight months before his successor, Kim Campbell, faced voters.

Now Liberal rivals will campaign on what they’d do differently, while Mr. Trudeau tries to show strength in the face of Mr. Trump’s threats. The new Liberal leader won’t have much time to establish their own identity as prime minister before an election campaign is triggered.

The timing almost rules out some potential contenders. Dominic LeBlanc can’t easily justify dropping his duties as Finance Minister and border czar now. The front-runners are Chrystia Freeland, who spent five years as Mr. Trudeau’s deputy PM before her explosive resignation that marked Mr. Trudeau’s end, and former Bank of Canada governor Mark Carney, who has never run for office. All face polls that suggest the Liberals will be clobbered by Pierre Poilievre’s Conservatives.

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Mr. Trudeau’s resignation would have looked very different in the summer of 2023, when he was sliding in polls but might have pointed to a legacy including the Canada Child Benefit or the renegotiation of the North American free-trade agreement – without such a deafening clamour for him to quit.

Mr. Trudeau’s own almost-tearful explanation of his belated decision to resign – that he is a fighter and was set to fight on until internal Liberal divisions made it impossible – is true, as far as it goes.

He thinks of himself as someone who fights through adversity. He had stared past Liberal MPs who suggested it was time for him to go – until they mobilized en masse to force him out.

Those MPs knew that it wasn’t the willingness to fight that Mr. Trudeau had lost, but rather the ability to persuade Canadians he could build common ground.

In 2015, his political identity was built around bridging divisions. He promised more people would benefit from economic growth, Indigenous reconciliation and climate-change action that would allow resource development. His political gift was instilling hope that such things were possible. His popularity with Canadians rose and fell with the notion that he was a unifier – or a divider.

Once, people were shocked when Mr. Trudeau inadvertently elbowed New Democratic MP Ruth Ellen Brosseau during a feisty 2016 Commons debate. The SNC-Lavalin affair that brought the resignations-slash-expulsions of cabinet ministers Jody Wilson-Raybould and Jane Philpott were another blow to the image. The unifying boost of leading the country in the COVID-19 pandemic gave way to divisions over vaccine mandates.

Many other things caused a lot of wear and tear, of course. Big spending, poor controls, immigration mismanagement, ArriveCan, high housing costs and especially inflation. Mr. Trudeau seemed to think he could still fight through it all when he’d lost so much ground that he was nearly standing alone.

At his news conference Monday, you could still hear Mr. Trudeau suggesting he could win over the country, even now, if it weren’t for the fact he can’t win over Liberal MPs.

He held on till the options ran out.