New Delhi, May 15 -- Having DISCOVERED the costs of tariffs, President Donald Trump has now discovered the costs of war. On March 9th he declared that his campaign against Iran would be over "very soon", sending oil prices, which had peaked at nearly $120 a barrel the day before, crashing to nearly $80 (before the war they had been $70). Iran's de facto closure of the Strait of Hormuz has blocked roughly 15% of global oil supply. Mr Trump, facing midterm elections and voters weary of inflation, is signalling that he cannot bear those costs-just as he retreated from his trade war after markets buckled last spring.

Yet Mr Trump is as chaotic in matters of war and peace as he is in economic policy. As we published this, the strait remained ...