Canada-U.S. partnership will endure beyond Trump clashes and tariff threats, says outgoing U.S. ambassador

Open this photo in gallery: Outgoing U.S. Ambassador to Canada David L. Cohen speaks to the Globe and Mail's editorial board on Dec 3.Fred Lum/The Globe and Mail U.S. president-elect Donald Trump's promise to impose wide-ranging tariffs on imports from Canada poses a potentially existential threat to this country, the departing U.S. envoy to Ottawa is warning. Mr. Trump has pledged a major change in American relations with Canada, beginning with the imposition of 25-per-cent tariffs aimed at both this country and Mexico, unless the two countries take action against what he calls an "invasion" of drugs and migrants entering…