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.”

Much of the world has been seeing Trump’s fixation with annexing Canada as a joke, or merely bluster, but Canadian leaders are taking it very seriously.