Dusk falls on Park Avenue in Manhattan on Thursday and Robert Rubin, the former US Treasury secretary and new chairman of Citigroup, sits in his comfortable office stuffed with the evidence of a prosperous and achievement-filled life. Here are plaques from his time in government, here a framed copy of him on a Time magazine cover and there a photograph of a fish he caught in Tierra del Fuego.

Mr Rubin is mulling the awkward question of how much responsibility he bears for the deep problems at one of the world’s biggest banks. Chuck Prince, Citi’s chief executive, resigned this week as it announced a debt writedown of up to $11bn tied to the US subprime mortgage crisis. Difficulties at Citi and other banks spooked markets and prompted a further lurch in the dollar.