Mahmoud Ahmadinejad must be wondering what went wrong. When he launched his re-election campaign last month he was the clear favourite to win. He appeared to have the support of Ayatollah Ali Khamenei, the Supreme Leader, and the backing of key institutions such as the Revolutionary Guards and the Basij militia. He has visited every province in the country twice, where he has dispensed government handouts to the poor.

His main opponent, Mir Hossein Mousavi, seemed to lack charisma. His reformist supporters looked disillusioned and his bid for the presidency doomed.

All that has now changed. Mr Ahmadinejad suddenly looks vulnerable. He is being widely criticised, even ridiculed in public, in a manner the regime would normally not tolerate. Yesterday he even accused his opponents of behaving like Hitler’s propaganda chief Joseph Goebbels — quite an allegation from a man who denies that the Holocaust happened.

Opposition to him is growing among the ruling clergy after he publicly maligned Hojatoleslam Ali Akbar Hashemi Rafsanjani, the powerful head of the Expediency Council. Hojatoleslam Rafsanjani has demanded an apology. His case has received support in an open letter from 50 clerics in the holy city of Qom.

What began as a straightforward contest has degenerated into an ugly and close-fought battle, exposing fault lines in the regime’s leadership.

Mr Ahmadinejad is hoping that his supporters will turn out in force tomorrow and that he can win in one round. A big turnout should favour Mr Mousavi. He has a real chance of winning if the vote goes to a second round.

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