Jon Chait is pessemistic about the government actually being overthrown in Iran. "For a revolution to succeed, it generally needs one of two things to happen: Either it needs its own weapons, or it needs mass defections by the state security force," he writes. But as Iran specialist Abbas Milani argues in a piece on our site today, there is an armed faction in Iran that has a stake in this fight:
When people defied Khamenei's orders by gathering en masse on Monday, the regime's armor of invincibility--so central to the regime's authoritarian control--was cracked. Without it, the regime cannot survive, and reestablishing it can come only at the price of great bloodshed.
But if Khamenei wants a crackdown of this magnitude, he will have to turn to the Iranian Revolutionary Guard Corps (IRGC)--a move that brings its own political costs. The IRGC was created by Khomeini shortly after the Islamic revolution as a more ideological and loyal alternative to the traditional military. The IRGC gradually became a force in its own right...
The IRGC has largely accepted the leadership of the clergy and Khamenei's role as commander in chief. But while Khomeini strictly kept them out of politics, Khamenei has encouraged them to get involved in his political battles. ... The rise of Ahmadinejad, himself once a member of the IRGC and reportedly an engineer in its infamous Al-Quds Brigade, has further encouraged the IRGC to seek an increasing share of political power.
It is difficult to imagine the IRGC quelling the current protests and then simply turning power over to the clergy. If a political compromise cannot be reached between the regime and the opposition, and the IRGC is used in suppressing the protests, its commanders would likely expect a bigger role in the government. It is even conceivable that faced with irresolution among the clergy, they will act on their own, and establish a military dictatorship that uses Islam as its ideological veneer--similar to Pakistan under Muhammad Zia-ul-Haq.
It's worth reading the whole piece, particularly Miliani's tracing the increasing politicization of the IRGC. They may actually have the power to launch a successful revolution--though it may not be the revolution Chait has in mind.