Why Steal the Election?

| Mon Jun. 15, 2009 10:20 AM EDT

Here's a quick question I haven't really seen anyone address regarding the Iranian election.  Assuming that the conventional wisdom is correct and it was stolen, why did they do it?  If Ahmadinejad stole it on his own, that's easily explainable as a pure coup/power play.  But if the clerical regime went along — which seems likely — what was it they were afraid of?  Mousavi was hardly the first reformist to run for president, after all, and he wouldn't have been the first to win.  What, precisely, was the threat that Mousavi presented to them?