He isn’t the first Republican president to try to walk this line between his party’s free-trade principles and populism. When President George W. Bush imposed similar tariffs in 2002, he did it against the advice of many of his advisers, and at the benefit, he argued, of struggling steel plants in states such as West Virginia, Ohio and Pennsylvania. (Bush lifted the tariffs a little more than a year later when Europe threatened a trade war.)

Trade is one of those issues that doesn’t fall neatly along political fault lines. But it’s rare that an issue divides a party in such stark ways. And for all of Republicans’ disagreements with their president, this is one on which they may never be able to see eye to eye.