After some moral victories over nuclear matters, America’s hardest test looms

TO HEAR Barack Obama talk about the “unprecedented threat” that terrorists might one day set off a nuclear bomb, it would be easy to assume that little has changed since the days of George Bush. But having adopted his predecessor’s diagnosis, Mr Obama is proposing a different treatment. Where Mr Bush disliked arms treaties and favoured muscular unilateral action—he invaded Iraq on the grounds that he could not afford to wait for proof of Saddam Hussein’s (non-existent) banned weapons to come in the form of a “mushroom cloud”—Mr Obama is performing an intricate multilateral dance.

His introductory bow came in Prague last year, when the president set out his vision of a world free of nuclear weapons. Then, in September, he held out his hand to Russia by announcing a reconfiguration of America’s anti-missile defence system. The couple’s twirl concluded last month with an agreement to cut each side’s nuclear arsenal to 1,550 deployed warheads. …