When asked whether he was quitting the Bush administration because it would be good for his political future, Rob Portman, the outgoing budget director, replied: “It would be good for my mental health.” Although Mr Portman was joking, a growing list of officials have already acted on that impulse.

At least 20 senior aides have left important posts in the White House, Pentagon or State Department over the past six months, as chaos has deepened in Iraq. “There’s a real sense of fatigue and very little sense of purpose,” said a senior official, who asked not to be named. “My guess is you’re going to see a lot more departures.”