For anyone who has spent time living in Canada, the country’s default posture towards its southern neighbour has long felt almost hard-coded: polite, deferential, almost allergic to confrontation. I saw this first-hand as a visiting scholar in the country in the early 1980s, when I met locals who embodied the national stereotype of moderation in all things. Canadians preferred compromise even when they had a right to push back, treating their far larger ally as a partner to be accommodated, not...