A unified North American trading powerhouse has long been seen as a potential bulwark against China. But Trump has repeatedly threatened to take over Canada and has targeted Mexico with some of his toughest tariffs. New Canadian Prime Minister Mark Carney has warned that his country’s traditional relationship with Washington is over.

By acting on his own, President Trump has broken with more than 200 years of U.S. history in which Congress set the direction of trade policy.

The trade war between the world's two largest economies is escalating as China on Friday slapped a 125% tariff on U.S. goods in response to President Donald Trump's 145% tariff on Chinese products. Caught in the crosshairs are businesses that are part of the more than $582.