That's how I felt after hearing that Ahmadinejad won in a landslide.
There is no doubt in my mind that Khamenei stole the election for Ahmadinejad. This is a new step in Iran calcifying into a counter-revolutionary state. A section of the ruling elite (which both Moussavi and Karoubi are a part of) have been effectively thrown out. It will be interesting to see how Rafsanjani responds- he was apparently the muscle behind Moussavi. There are conflicting reports on what he's up to, check John Marshall's reporting here.
The most plausible explanation for what happened was given by Juan Cole, who's blog, informed comment, has been indispensable for understanding the election. Here is his recreation of what happened:
"As the real numbers started coming into the Interior Ministry late on Friday, it became clear that Mousavi was winning. Mousavi's spokesman abroad, filmmaker Mohsen Makhbalbaf, alleges that the ministry even contacted Mousavi's camp and said it would begin preparing the population for this victory.
The ministry must have informed Supreme Leader Ali Khamenei, who has had a feud with Mousavi for over 30 years [anyone have more info on this?], who found this outcome unsupportable. And, apparently, he and other top leaders had been so confident of an Ahmadinejad win that they had made no contingency plans for what to do if he looked as though he would lose.
They therefore sent blanket instructions to the Electoral Commission to falsify the vote counts.
This clumsy cover-up then produced the incredible result of an Ahmadinejad landlside in Tabriz and Isfahan and Tehran.
The reason for which Rezaie and Karoubi had to be assigned such implausibly low totals was to make sure Ahmadinejad got over 51% of the vote and thus avoid a run-off between him and Mousavi next Friday, which would have given the Mousavi camp a chance to attempt to rally the public and forestall further tampering with the election."
- Friedman