In fact, the economic objectives are internally contradictory. On the one hand, Trump says that the dollar is over-valued, and this has impeded America’s competitive position in global markets. But on the other, the imposition of tariffs tends to worsen this problem because it raises the value of the dollar and thereby the price of US goods.

The president, who has threatened and delayed other tariffs, said he will announce the new measures Monday. Canada and Mexico are among the U.S.’s top steel suppliers.