“He started it,” is playground justice. It may soon be America’s trade policy. 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. A memorandum directs federal agencies to look into “non-reciprocal trade arrangements”, including value-added taxes (VAT) and non-tariff barriers, and to report on remedies by April 1st. Like teachers tasked with adjudicating a squabble, American officials now face the unenviable task of working out which trade partners are the worst behaved.