The costs to the U.S. of poisoning its relationship with Canada are measurable. We see them in high U.S. inflation, the billions lost to U.S. tourism, disrupted trade with border states dependent on the Canadian market, a major hit to the bottom line of Detroit’s automakers, and the collapse of exports for the American booze industry.

Increasingly, Americans with the most to lose from a continental rift are pushing back, reports Tim Shufelt of the Globe and Mail.

A few weeks ago, the United Steelworkers – one of the largest private-sector unions in the U.S. – made waves when it broke with Mr. Trump over his treatment of Canada, saying the latest tariff threats could “drive a further wedge between our nations.”

U.S. automakers have also been quietly pressing the case that tariffs harm their competitiveness. Tariffs cost them US$12.5-billion last year alone, according to one report. New rules requiring a minimum of 50-per-cent U.S. content to qualify for lower tariffs would add another US$2-billion in annual costs for each company, according to another.

Canada has more friends in American business and politics than perhaps we realize. A slew of American policymakers have also recently spoken up in Canada’s defence after Mr. Trump’s latest tariff salvo.