Donald Trump has incoherent and unhinged beliefs about trade policy. He also has a penchant for pretending to be a “crazy guy” for the sake of increasing his leverage in negotiations. This made it difficult to tell whether his proposal for an across-the-board 25 percent tariff on Canadian and Mexican imports was sincere.

Some Canadian politicians previously suggested tossing Mexico from a three-nation trade agreement with the United States.

Uncertainty surrounds the trade war touched off by Trump’s tariffs. But some of the basics are taking shape.