While I’m very pleased to watch internal political strife undermine the legitimacy of Islamic theocracy in Iran, I think we really need this stop a minute, take a deep breath, and ask ourselves why we should be backing either faction.
Neither is friendly to American policy in the Mideast (Mousavi is one of the chief supporters of Hamas in Iran), both support continuation of the Iranian nuclear program, and neither envisions any kind of fundamental reform of the Iranian political system to something closer to western secular democracy.
The biggest difference between them is that they represent somewhat different factions of the reigning Iranian political elite: Ahmadinejad represents the portions of the military and clerical establishment who believe that Islamic revolutionary purity mandates massive redistribution of resources toward the poor (you can think of him as sort of a Iranian Chavez in this respect), while Montazeri represents a sort of quasi-fascistic fusion of the most corrupt segments of the Iranian Rich, the massive business interests of Revolutionary Guards, and the worldly segments of the clergy.
Both groups are somewhere between political parties and mafias, and neither group has any interest at all in surrendering power to something more close resembling a representative government, in terms of advancing American interests in a very real sense we might as well be trying to choose for example between various factions of Hamas or Hezbollah. All we can be certain of is that if we try to back one faction over the other were are unlikely to be satisfied whatever the outcome, so the smart thing to do is to produce general statements of support for the will of the Iranian people (and indeed, the will of large numbers of Iranians will be thwarted whatever the outcome) without trapping ourselves into appearing to the Iranian people to be backing either faction of their oppressors.
Which, it seems to me, is pretty much the current US policy, and IMO the best of the bad choices under the circumstances.
I’m not backing either one. I want to see strife, riots, civil war. Let them destroy their infrastructure before they get nukes.