Iran’s disputed election and the government’s suppression of the widespread protests that followed it pose a challenge for US diplomacy. Barack Obama had only just embarked on a policy of engagement with Iran’s ruling regime. As recently as March, he offered it a “new beginning”. That regime now stands discredited – even more than it already was – in the eyes of millions of Iranians and much of the world.

The US administration’s hesitant tone of recent days is understandable. To take sides unreservedly with the protesters, condemning the conduct of the election and its aftermath, and threatening reprisals, would kill the new policy and any hope of achieving its aims at birth. Whether he likes it or not, Mr Obama may have to do business with Mahmoud Ahmadi-Nejad. Entangling the US in Iranian politics, moreover, would be unlikely to serve the interests of the regime’s opponents. It might well strengthen its leaders and provide an excuse for greater brutality.