The conventional thing now is to warn of a trade war, and last week Christine Lagarde, the Fund’s managing director, gave a speech in Hong Kong warning of “darker clouds looming” because of rising trade tensions. If protectionist forces prevailed it would be “an inexcusable, collective policy failure”. (The speech, by the way, was entitled “Fix the Roof While the Window of Opportunity is Open”, which suggests a rather dodgy way of trying to repair a roof by leaning out of a window, but you can see what she means.)