On February 13th Donald Trump announced he had decided, for what he later called “purposes of fairness”, to employ reciprocal tariffs. When the levies will go into effect, and how they will apply, is uncertain.

If the US genuinely tries to close its overall deficit with big tariffs all round, it will cause a crunching recession. If Trump discriminates between trading partners, the heavily tariffed ones can nip through the side door of those who escaped more lightly.

Donald Trump’s tariffs are a headache for all his trade partners. But the U.S. president’s plan to impose ad hoc “reciprocal” levies on imports are a particular problem for the European Union. By enabling him to target whichever countries in the bloc he pleases,