The Prime Minister of a parliamentary democracy is selected from the members of parliament by the party with the most seats. The Conservatives, Canada's far-right party, campaigned on making Pierre Poilievre, their leader and an existing member of parliament, Prime Minister if they won the most seats in yesterday's election. The Liberals, Canada's center-right party, campaigned on keeping Mark Carney, their leader, as Prime Minister.

The Liberals won, so Carney will continue to be PM until he steps down or a different party is elected to more seats than the Liberals. Poilievre, on the other hand, couldn't retain his seat in Parliament, so even if the Conservatives had won the most seats, he couldn't be PM.

Imagine if the US President had to be a Senator and Kamala Harris had lost her Senate seat while trying to campaign for the Democrats to get a majority in the Senate and make her President.