With no NAFTA deal or regard for international trade rules, there is little to stop a petulant and vengeful president from introducing tariffs on other Canadian exports, or from obstructing cross-border flows of goods and people.

Trump may have started this, but no matter what action Canada takes, Trudeau won’t finish it. Americans will, one way or another. In the meantime, Canada must do its part to keep this trade dispute from escalating to a full-on trade war.