It has been a week of dramatic developments in Tehran. Since Monday, we have seen a series of demonstrations larger than any since the revolution of 1978-79.
The question now is where the popular anger will lead. If the demonstrations continue, and especially if there are more injuries and deaths, the hardline leadership will come under even more intense pressure. They have already made concessions such as the Supreme Leader's announcement of an investigation into the conduct of the election and the announcement of the Guardian Council that they are ready to recount at least some of the disputed votes. But many of the demonstrators say that these are simply delaying tactics.
After the announcement of the outcome of the election, Mousavi had a dilemma about how to handle the result; now it is Khamenei who has a dilemma about how to handle the demonstrations. More deaths will in all probability only sharpen the anger of the demonstrators and sap his own support within the ruling elite.
There are rumours already that some senior clerics (not just long-term opponents like Ayatollah Montazeri, but also less obvious critics like Ayatollahs Samei and Golpayegami) are calling for the election to be annulled. There are also rumours of a split within the security forces – that some Basiji militia have refused to act against the demonstrators, and that elements within the Revolutionary Guard are also unhappy at the regime's behaviour.
These are only rumours. It is possible that Khamenei and his leadership circle may yet succeed in upholding the results. But if the momentum of events continues to swing in favour of Mousavi, they may need to reassess where their true interest lies. Last weekend Ahmadinejad described the opposition as "layers of dust", or flotsam and jetsam. But it may turn out that he is the flotsam and jetsam, and that the ruling group may come to see Mousavi as the only lifebelt that can save the Islamic Republic from sinking.
The writer is director of the Centre for Persian and Iranian studies at Exeter University and author of Iran: Empire of the Mind