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Last night Tehran was seized by tense confusion: at first, both the incumbent, Mahmoud Ahmedinejad, and his reformist rival, Mir Hossein Mousavi, claimed victory in the presidential election. Later, and with suspicious rapidity, the electoral commission pointed to a landslide victory for Ahmedinejad. Mousavi and his supporters had insisted before that any outcome other than their victory could only have been achieved through vote rigging.

A crescendo of electoral mania has struck Tehran over the last week as Iran witnessed the biggest mobilisation of people since the events of the 1979 revolution, with massive crowds marching in support of both Ahmedinejad and Mousavi. While Ahmedinejad clearly does enjoy popular support across the country, the extreme margin and rapidity of his...