This is MUST READ piece by Kim Kagan, President of The Institute For The Study of War. There's no one in my opinion who knows the details on the ground in Iraq more than her. I think you'll find most interseting is what she has to say about Mr Sadr. Here's two paragraphs I chose from the article:
The Iranian-trained militias operated in 2006-2008 as units known as Special Groups or Secret Cells, ostensibly claiming to serve within Mr. Sadr's militia. In reality, the U.S. military says their titular leader – the ex-Sadrist Qais Khazali – reported to a Lebanese Hezbollah commander, who in turn reported to the highest Qods Force leaders.................
Iran and Mr. Sadr could not simply unleash a floodtide of violence that would overwhelm Iraqi Security Forces partnered with U.S. units, because they are more capable of handling the situation. For all of his nationalist rhetoric, Mr. Sadr is evidently not in control of his movement -- it appears that the decision to fight or not rested with the Qods Force commander and not with him. But Mr. Sadr's militia remains a reserve from which the Special Groups can and will draw in crisis.
~Post by Mel