Pierre Poilievre, leader of Canada’s Conservative Party, seemed set to become Canada’s next prime minister at the start of 2025. For more than a year, his party had a 20-point lead in opinion polls over then-Prime Minister Justin Trudeau’s Liberal Party and momentum toward a landslide victory. Then came President Trump. Trump’s trade war and threats to annex Canada have upended Canadian politics. In less than three months, the Conservatives have gone from heavy favorites to underdogs in an election set for April 28. Poilievre’s problem is bad timing. His preferred foil, the unpopular Trudeau, resigned in March, when Trump’s...