The leaders of Mexico and Canada responded quickly, and in different ways. Justin Trudeau, Canada’s prime minister, jumped on the phone to Mr Trump to chat about the “intense and effective connections” between their countries. His deputy, Chrystia Freeland, released a statement about the importance of border security.

The president-elect’s opening salvo in trade and border talks with the United States’ neighbors is casting a harsh light on the North American alliance.

The magnitude of this tariff doesn't justify changing our economic forecast. But businesses involved in imports and exports must pay close attention to the details.