Mousavi, his wife (artist Zahra Rahnavard), and former parliament speaker Mehdi Karroubi -- all Green Movement stalwarts -- have been under house arrest since the large street protests of February 2011. Repression has not abated -- on the contrary (see, for example this report in the Guardian. And that also spilled over to the Ahmadinejad camp; even pro-Ahmadinejad clerics have been rounded up or arrested by security services in some provinces, and five websites campaigning for Mashaie were shut down.
All VPNs (virtual private networks) have been closed down at myriad of Iranian Internet cafes, and Internet speed has been slowed to a trickle.
Even if all this "prevention system" works; and even if the Supreme Leader has his way (and winning candidate, possibly Qalibaf), the outlook is not pleasant. The post-Ahmadinejad incumbent will inherit an ultra-fragmented political landscape; a lot of people blaming the government's appalling management as well as international sanctions for their plight; and the same hardcore hostility displayed by the US, Israel and the Sunni axis. Hangin' on in quiet desperation seems to be the popular Iranian way.
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