A decision to bomb Iran would be a war of choice. If Mr Trump scores what looks like an easy victory, without ground forces, he is likely to be hailed as a forceful leader. If he lands the country in a regional quagmire and the price of oil soars, the public verdict will probably be harsh. ■

The prospect of a U.S. strike against Iran has exposed divisions among Trump supporters, with part of the rift on full display when Tucker Carlson, on his streaming program, clashed with Republican Senator Ted Cruz.