Also not encouraging: The Trump White House explanation for the ban — to protect workers — is an evidence-free mess. Past government efforts to restrict immigration during downturns give little reason to expect success this time around. During the Great Depression, there were state and local efforts to repatriate Mexican workers, with some 400,000 to 500,000 eventually sent home. But the places that lost their Mexican workers either did no better than other cities and regions, or did worse.

A 2017 paper “The Employment Effects of Mexican Repatriations: Evidence from the 1930’s” found that the “repatriation of Mexicans, who were mostly laborers and farm workers, reduced demand for other jobs mainly held by natives, such as skilled craftsman and managerial, administrative, and sales jobs.” Similarly, the early 1960s exclusion of some 500,000 seasonal Mexican workers to boost wages, mostly in the farm sector, also failed.

But is the ban really about economics, especially since the evidence so clearly points in the other direction? What more vivid example does Trump need of its stupidity than his attendance at the recent rocket launch by SpaceX, a company founded by immigrant Elon Musk?