Noah Millman’s post is worth a read. An excerpt:

If the regime survives by brute force, it will be revealed to be relatively weak in terms of popular support and will be less credible globally than it was before. If the regime simply waits the protests out, then very little will have changed at all. If the regime survives by abandoning Ahmadinejad, then it will be focused on maintaining its credibility internally, and Mousavi will not be in a position to go off the reservation much if at all – so negotiations with America, if they happen will not really go anywhere. If the regime does not survive, it will be because the military turns on it decisively (which I would be really surprised by), and whatever regime emerges to replace it will have to establish its own credibility as a patriotic guardian of the Iranian people. That means no dramatic rapprochement with America, whatever happens behind the scenes.

Update: You can comment on Millman’s argument, and the Iranian situation generally, at my Washington Post page.