New Delhi, Aug. 25 -- BREWER, Maine - Canada entered the week holding a security guarantee it had never thought to question and a trade pact its government spent years negotiating. By Monday, it could rely on neither.

the United States' military protection of Canada was contingent, not unconditional. "Canada is a country that has underinvested in its military that quite literally would get invaded by a foreign country were it not for the umbrella of protection provided by the United States of America," Vance told the audience. He did not name which country.

The remarks arrived as 50 percent tariffs on roughly $20 billion in Canadian goods took effect the previous Saturday, the latest escalation in a trade confrontation that has now brok...