After a typical White House day of chaos and indecision, Donald Trump overnight announced the most dramatic moment of US protectionism in decades: the imposition of 25% tariffs on steel imports and 10% on aluminum.

The tariffs, which are higher than earlier forecast, will almost certainly spark retaliatory measures from countries affected by them. The top five steel importers for the US are Canada, Brazil, South Korea, Mexico and Russia. China is the 11th largest importer, and already subject to restrictions imposed by Trump. Australia is a small player in the US market, but BlueScope Steel exports around $170 million a year there, and Malcolm Turnbull lobbied furiously during his Washington trip last week for Australia to be exempted. BlueScope, however, will also benefit from the tariffs, because it owns a major steel maker called North Star in Ohio and has controlled 100% of the business since late 2015, generating hundreds of millions of dollars in profits.