Trump’s No. 1 Canadian Enemy: Doug Ford Relishes Antagonist Role

The premier of Canada’s most powerful province — and arguably the country’s most successful politician today — has gotten under Donald Trump’s skin again.

An anti-tariff ad launched by Ontario Premier Doug Ford’s government prompted Trump to lash out Thursday night, announcing all trade negotiations with Canada had been halted. The ad uses excerpts from a 1987 speech by former President Ronald Reagan, in which he defended free trade and criticized the idea tariffs lead to economic gains.

Trump’s eruption followed his more muted reaction earlier in the week, when he said, “If I was Canada, I’d ...