George Washington carried a musket. Franklin Roosevelt sent in heavy bombers. But for President Barack Obama, who must reconcile a weary American public with the demands of an increasingly unstable world, the armament of choice has been a weaponised form of finance.

To hear enthusiasts describe them, economic sanctions are trusty swords. By excluding hostile governments and their senior officials from western financial markets, America and its allies can pursue diplomacy with a streak of coercion. The number of US sanctions programmes has doubled in recent years, and they now target the personal assets of a rogue state’s political and economic elite.

Jack Lew, US Treasury secretary, has called this “a new battlefield for the United States, one that enables us to go after those who wish us harm without putting our troops in harm’s way”. Yet sanctions cannot solve as many problems as their champions appear to believe, and overusing them is risky.