In President Trump’s unpredictable handling of sweeping tariffs on friendly nations, Canada stands out.

Despite the apparently positive atmosphere in talks, and the unusually warm relationship between Mr. Trump and Prime Minister Mark Carney of Canada, the country has still been on a wild ride.

In just three weeks, Canada went from a friendly meeting between the two leaders and the goal of reaching a trade deal on July 21, to a brief suspension of talks and then, late on Thursday evening, a threat by Mr. Trump of yet higher tariffs and another delay in talks.

As Mr. Trump upends the global trade order, good vibes appear necessary but still not enough to clinch a deal.

Canada — America’s next-door neighbor, top trading partner and a close defense ally — was the first target of Mr. Trump’s sweeping tariffs, alongside Mexico, as soon as he won the election. Mr. Trump justified the tariffs using debunked claims that Canada was allowing fentanyl and illegal immigrants to flow into the United States. He also said that he wanted to annex Canada and make it the 51st state.

Mr. Trump’s acrimonious relationship with Canada’s former prime minister, Justin Trudeau, seemed to further stoke the negative atmosphere. Then, in the spring, the vibe appeared to shift.