Mark Carney drew international attention as Canada's prime minister by warning that middle powers must resist economic coercion by more powerful countries. Now President Donald Trump is putting that warning to the test with sweeping new tariffs that could show how much economic pain Canada can absorb.

Tensions escalated late Friday when Canada walked away from negotiations after Carney concluded the United States was demanding too much in exchange for tariff relief. The U.S. imposed 50% duties Saturday on about $20 billion worth of Canadian goods, and Carney announced dollar-for-dollar retaliation beginning Sept. 8.