This is the beginning of making America rich again,’ president says.

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.

Trump signed proclamations raising the U.S. tariff rate on aluminum to 25% from his previous 10% rate and eliminating country exceptions and quota deals. The measures will take effect on March 4.