Canadians on Monday started voting to choose a prime minister who will negotiate with President Trump over trade and security, and to navigate their economy through turbulence as businesses freeze spending and hiring.

The Conservative Party was once considered the heavy favorite in Canada’s election. But President Trump’s trade war has upended the campaign, with the Liberal Party surging.

Canadians will vote for a candidate from one of the political parties in their federal “riding,” or district. Whichever candidate gets the most votes in a riding will become a Member of Parliament (MP) in the House of Commons, and the party with the most MPs wins the election.