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* A third faction believes that the entire Khomeinist system has passed its sell-by date and that Iran is ripe for regime change in the same way that the Soviet bloc countries were in the late 1980s. This faction is led by people like former Interior Minister Abdallah Nuri (a mid-ranking cleric), former rector of Tehran University Muhammad Abbas Sheybani and former members of parliament like Mahmoud A'alami and Imadeddin Baqi.

It now seems likely that Mehdi Karrubi -- a mullah who was another of the three losing candidates -- may also be joining them. In a statement published in Tehran yesterday, Karrubi claimed that Khamenei's nomination as "Supreme Guide" in 1989 had also been "a fruit of fraud" -- an implicit call for him to step down.

The rigged election has also split the military. The third losing candidate was Gen. Mohsen Rezai Mir-Qaed -- who led the Islamic Revolutionary Guard Corps for 16 years.

Rezai's humiliating defeat -- in an election widely viewed as rigged -- has angered many Guard officers, who see him as something of a father figure. Defense Minister Gen. Mustafa Muhammad Najjar has praised Ahmadinejad in public -- but the commander of the Revolutionary Guard, Gen. Ali Jaafari, has maintained a meaningful silence. More, he has refused to send in Guard units to crush demonstrations in Tehran and 16 other major cites.

Since Ahmadinejad owes his ascent to support from the military-security establishment, any split in the Guard and its allied organs could spell trouble now.

Some compare the current popular unrest with the riots that shook Iran during Muhammad Khatami's presidency. But there are a number of key differences:

* Khatami was not as unpopular personally as Ahmadinejad is. Thus, Khatami was always able to act as a bridge between protestors and the "authorities."

* Back then, Khamenei managed to stay above the fray -- thus preserving the system's prestige, if not any actual popularity. This time, he has (for reasons hard to fathom) jumped in the ring in support of Ahmadinejad.

* Today, some heavyweights of the regime are siding with the protestors -- shattering the unity of the Khomeinist establishment in the face of a popular challenge. With every day that passes the number of dignitaries declaring support for Ahmadinejad declines -- while the number of those calling for his dismissal increases.

* This protest movement isn't limited to students in major cities. There are numerous reports of unrest in small towns and villages across the country. In some places, like Marivan and Gohar-Dasht, people have attacked government offices, burning the portraits of Khamenei and Ahmadinejad and seizing control of ballot boxes.

However the current struggle turns out, the regime has lost a good part of its legitimacy. It is also made clear that peaceful evolution within the regime is not possible. This makes the "regime change" option attractive for the first time since the mid-1990s.

Amir Taheri's latest book is "The Persian Night: Iran Under the Khomeinist Revolution." New York Post