President Trump took exception last year when we called his tariffs against Canada and Mexico the dumbest trade war in history. It got dumber this weekend as Mr. Trump escalated with another round of border taxes on Canadian imports, a mere 10 weeks before midterm elections. …Mr. Trump’s threatened tariffs took effect Saturday morning. Canadian Prime Minister Mark Carney threatened to retaliate dollar-for-dollar starting Sept. 8. Both sides could still walk back from the ledge, though Mr. Trump’s escalation could make this harder for Mr. Carney politically since Canadians don’t like being bullied by Washington. …But Mr. Trump doesn’t want to update the deal. He wants to rewrite it unilaterally. … Republicans are already getting pounded on the campaign trail over his tariffs and inflation. One reason for Mr. Trump’s frigid approval rating is that voters believe Mr. Trump is waging blunderbuss wars without a strategy, and on trade they’re right. [to access the full story a WSJ subscription is required]