Sure, Mr Obama has made mistakes. While promising that all options are on the table, he has let successive defence secretaries say that bombing Iran would be futile and dangerous, which may be true but blurs the message. He also fumbled his response to the popular demonstrations that followed Iran’s fraudulent presidential election of June 2009. Having worked hard to start a dialogue with the Iranian leadership, and calculating that the Green movement would not be able to topple the government, he was slow to denounce the crushing of the protests. That looked weak. But the Republican claim that this squandered an opportunity to fell the regime is questionable. In contrast to Egypt, where America had influence on both Hosni Mubarak and the army it had helped to equip, it had no serious leverage on the ground in Iran, and its verbal support might have damaged the credibility of the very people it was trying to help…

While Republicans accuse him of appeasing Iran, Mr Obama faces critics from the opposite direction who say his biggest mistake was to withdraw his outstretched hand too soon. In a thorough new history of the president’s engagement with Iran (“A Single Roll of the Dice”), Trita Parsi, the founder of the National Iranian American Council in Washington, DC, regrets Mr Obama’s failure to accept the proposal from Brazil and Turkey. Having chosen to pursue diplomacy and pressure simultaneously, he bet all the diplomacy on a single roll of the dice, and when that got nowhere was left only with the pressure—which may in time also fail. If diplomacy is ever to succeed, Mr Parsi says, America must not retreat at the first sign of Iranian intransigence or congressional opposition, both of which are inevitable. The trouble, he concludes, is that the 30-year enmity between Iran and America is no longer a phenomenon, “it is an institution”.