President Donald Trump ordered a 25% tariff on steel and aluminum imports, escalating his efforts to protect politically important US industries with levies hitting some of the country’s closest allies.

In slapping duties on steel and aluminum nearly seven years ago, Trump reached into the federal government’s tariff toolkit and pulled out Section 232 of the Trade Expansion Act of 1962. Section 232 gives the president the power to impose tariffs on other countries national security grounds.