The thing about populism is it usually involves doing things that are popular.

This is something that European nationalists and Latin American strongmen have long known. When they come to power, they aim to deliver concrete benefits to their supporters, even at the cost of their nations’ long-term fiscal health.

President Trump has delivered on some of the things he promised supporters on the campaign trail: He has appointed a conservative Supreme Court justice; begun more aggressive enforcement of immigration laws; and directed his appointees to slash regulations on fossil fuel and other industries. But in terms of spending, Mr. Trump has embraced the austere preferences of congressional Republicans, even when that approach has contradicted his campaign promises.

To see the tension, consider an alternate history of the Trump administration: one in which the president embraced the lessons of right-wing populists from abroad.

It’s Jan. 21, and Mr. Trump is newly sworn in. Shrugging off the snark from liberals on Twitter about the size of his inauguration crowds, he directs his staff to go to work on the Make America Great Again Act of 2017.