So since the surge, which had shown some success in decreasing violence, was going to have to wind down soon, the Iraqi government decided to go out and pick a fight with the Sadrists? I suppose they figured they'd better do it while the US Army is still there to back them up,but it seems like it's going to restart a Shia internecine war. This may make our hired guns the Sunnis happy at the moment, but Shiites are the majority of the population, and if they see this as targeting them the Sunnis will eventually pay. Besides, starting new fires when you've shown you can barely contain the ones already burning is asking for trouble.
Of course the Bush administration will now use this as an excuse to try to back off on troop withdrawals. I say try because they had to pretty much max out the army to get the surge, and slowing down withdrawals may well break things down. Not that the administration really cares. They want to pick at the Iranian bogeyman, and they'll grind the military into dust to do it. After all, it'll be someone else's problem in a year.