One question is why this is necessary even for public-health reasons. Mr. Trump has barred travel to the U.S. from much of the world, and his Administration has stopped processing nearly all new visas for foreigners. Foreign governments have suspended nonessential travel to the U.S. All of this plus mandatory 14-day quarantines for new arrivals should block any new coronavirus surge from overseas.

There’s also no evidence we’ve seen that immigrants are associated with the spread of Covid-19 more than anyone else. Hot spots for infection have broken out in big cities like New York, and in meat-packing plants in the Midwest, where immigrants locate. But the spread there is due to living, working or commuting in close quarters, not to larger infection rates among immigrants.

Mr. Trump’s economic case is even weaker. “Decades of record immigration have produced lower wages and higher unemployment for our citizens, especially for African-American and Latino workers,” Mr. Trump said in a White House statement Tuesday.

But only weeks ago Mr. Trump was boasting about a U.S. jobless rate of 3.5% and record lows for blacks and Hispanics.