Prime Minister Justin Trudeau of Canada rebuked President Trump directly on Tuesday over sweeping new tariffs and pledged to “relentlessly” battle to protect his country’s economy. “A fight with Canada will have no winners,” Mr. Trudeau said, just days before he is set to step down as prime minister.

Speaking at a news conference in Ottawa, the Canadian capital, and flanked by senior members of his cabinet, Mr. Trudeau labeled a trade war between the North American neighbors “very dumb” and portrayed Mr. Trump’s motives in attacking Canada, one of the United States’ closest allies, as furthering the territorial aggression that the American president has repeatedly expressed toward its northern neighbor.

“What he wants is to see a total collapse of the Canadian economy, because that’ll make it easier to annex us,” said Mr. Trudeau said, adding, “We will never be the 51st state.”

“When it comes to defending our great nation, there is no price we all aren’t willing to pay,” he said.

After U.S. tariffs of 25 percent on almost all Canadian goods took effect at midnight on Tuesday, Mr. Trudeau imposed retaliatory tariffs that amount to about $20.5 billion and has promised another $85 billion in tariffs in three weeks if the United States did not back down.

Mr. Trudeau, whose country is home to the largest Ukrainian diaspora outside of Russia, also raised questions about Mr. Trump’s foreign policy priorities in pursuing a deal to end the war started by Russia’s invasion of Ukraine.

Thank you for your patience while we verify access. If you are in Reader mode please exit and log into your Times account, or subscribe for all of The Times.

Thank you for your patience while we verify access.

Already a subscriber? Log in.

Want all of The Times? Subscribe.