Barack Obama enters his first real moment of global diplomacy in London on Wednesday with a paradox: he is the most popular US president in a generation, but you would have to go back more than two generations to find one with fewer cards to play.

Many outside the US accept that the country is not solely to blame for the global meltdown. None would point the finger at Mr Obama personally. But it is he who will be the target of long pent-up resentment at the US’s evangelical approach now that its belief in self-regulating markets has been discredited.