Pres. Trump's threat to double import tariffs on Canadian-made vehicles and part is either a savvy negotiating ploy or just bluster. It could be a little of both.

The president announced the new levies, effective Jan. 1, after Canada said it would retaliate against duties the U.S. implemented over the weekend.

President Donald Trump threatened to double tariffs on Canadian cars on Monday, the latest sign that the United States and Canada are barreling toward a deeper trade war after…