President Trump campaigned on a promise to “build a great, great wall on our southern border.” After he was inaugurated as president, his administration said it was considering taxing imports from Mexico to cover the estimated cost of $21.6 billion. (That Department of Homeland Security estimate is roughly double Trump’s price tag of $8–$12 billion; others peg the cost much higher). Many economists were quick to note how such a tax would raise the cost of Mexican goods in the United States and violate Trump’s other campaign promise to “make Mexico pay.” In practice, Americans would pay twice: up front for the wall, and again in the form of higher prices for Mexican goods.