So far, there are no such reservations at the soldier-to-soldier level. Canadian defence officials say their senior American counterparts are queasy about Mr Trump’s efforts to hobble an ally. “They’re horrified,” says one. “They know that weakening your allies emboldens and opens doors for your enemies.”

The U.S. president on Tuesday reiterated his claims on Canada’s territory as he increased tariffs, threatening to bring the country’s economy to its knees.

Trump and his aides have reportedly threatened to redraw the northern border, go after Canada’s minerals and water, and cancel NORAD.