TORONTO — Canadians will vote for a new government Monday in an election that has been upended by U.S. President Donald Trump’s trade war and his threats to make Canada the 51st state.

Prime Minister Mark Carney and the governing Liberal Party appeared poised for a historic election defeat until Trump slapped heavy tariffs on Canada and began threatening its sovereignty.

Trump’s attacks have infuriated Canadians, who are canceling trips to their southern neighbor and avoiding buying American goods when they can. The surge in Canadian nationalism has bolstered the Liberals’ poll numbers.

The opposition Conservative Party had hoped to make the election a referendum on former Prime Minister Justin Trudeau, whose popularity cratered as food and housing prices rose and immigration surged. But after decades of bilateral stability, the vote is now expected to focus on who is best equipped to deal with Trump.

How will the election work?

Voters nationwide will elect all 343 members of the House of Commons, one for each constituency. There are no primaries or runoffs — just a single round of voting.

The candidate who finishes first in each constituency will be elected, even if they don’t get 50% of the vote.

This has generally cemented the dominance of the two largest parties, the Liberals and Conservatives, because it’s difficult for smaller parties to win seats unless they have concentrated support in particular areas.

How is the prime minister chosen?

The party that commands a majority in the House of Commons, either alone or with the support of another party, will form the next government and its leader will be prime minister.

Carney replaced Trudeau, who announced his resignation in January but remained in power until the Liberal Party elected a new leader, Carney, on March 9.

Carney was sworn in as Canada’s 24th prime minister March 14. He hopes to retain the job and avoid becoming one of Canada’s shortest-serving prime ministers.

Who is running?

Carney, 60, is one of the two main candidates. He successfully navigated financial crises when he headed the Bank of Canada and later ran the Bank of England, becoming the first non-U.K. citizen to do so since its 1694 founding.

A highly educated economist, Carney worked for 13 years for Goldman Sachs in London, Tokyo, New York and Toronto, before being appointed deputy governor of the Bank of Canada in 2003. He has financial industry and public service credentials.

Pierre Poilievre, the leader of the Conservatives, is Carney’s main challenger. He and the party seemed headed for a big victory in the election until Trump’s near-daily trade and annexation threats derailed them.

Poilievre, 45, is a career politician and firebrand populist who says he will put “Canada first.”

There are two other parties that have official status in Parliament. If the Liberals or Conservatives secure the most seats in the House of Commons but fail to win a majority, they would need to rely on either the New Democrats, a progressive party, or the separatist Quebec party Bloc Québécois to pass legislation.

What will result mean for the United States?

Trump has threatened to slap steep tariffs on Canadian goods, and both Carney and Poilievre said that, if elected, they would accelerate renegotiations of the countries’ free trade deal in an effort to end the uncertainty hurting both of their economies.

Carney plans to diversify Canada’s exports and is reviewing the remaining purchase order of U.S. F-35 fighter jets to see if there are other options “given the changing environment.” Carney visited Paris and London, not Washington, for his first trips as prime minister.

But almost 80% of Canada’s exports go to the U.S.

“Let’s be honest, if Canada does a remarkable job — a remarkable job — of diversifying trade, what is that going to look like?” said former Foreign Minister John Baird, noting that even shifting 3% - 5% over five years would be quite an achievement.

“Let’s keep our eye on the main ball. They are 78% of our customers so we need to tackle that challenge,” said Baird, a Conservative who works as a senior adviser at a law firm.

What do the polls say?

In the latest Nanos poll, the Liberals led by 4 percentage points nationally and 6 points in Ontario, Canada’s most populous province. The latest poll had a 2.7-point error margin.