The tariffs are another case of the Administration playing political favorites. The American Primary Aluminum Association, which represents two aluminum producers, Century and Magnitude 7 Metals, sent a letter to Mr. Lighthizer in May calling for the reinstatement of tariffs on Canada. The U.S. has only six primary aluminum smelters.

Yet 97% of U.S. jobs in the aluminum industry are in downstream production or processing. The tariffs will raise costs for them as well as end-users like beer companies and auto makers. A Federal Reserve paper noted last December that Mr. Trump’s Section 232 and 301 tariffs in 2018 were associated with lower manufacturing employment and higher producer prices.

The pandemic’s uncertainty has burdened businesses, and border taxes won’t help. If the U.S. walks back on its trade commitments, how can it criticize China for doing the same? The aluminum tariff is Mr. Trump at his policy worst: He hurts U.S. industry and consumers, while telling America’s friends that his word on trade can’t be trusted.