Washington rang alarm bells this month when it invoked a law dating from the Korean war — the Defense Production Act — to order 3M to produce more of its sought-after N95 respirators. The White House and 3M finally agreed on a compromise in which the company will import 166.5m masks to the US from China, Singapore and South Korea in the next three months, but can continue exporting from the US to Canada and Latin America. In other cases where foreign buyers have pointed fingers at the US it is less clear whether the White House is directly to blame, or the frantic competition among US states which Mr Trump has left to fight it out for supplies. The tussles over ventilators and masks could spread further, into drugs found to be useful in treating Covid-19, and testing equipment as countries start to emerge from lockdown. Urging countries to show restraint in ordering only what they strictly need, and suppliers to avoid profiteering, may seem a vain hope.