As we know from Robert Alt, the battle started by Moktada al-Sadrs forces is not inspired by a burst of new anti-American sentiment. Instead, it springs out of internal Iraqi politics: as the transfer date approaches, Moktada al-Sadr is trying to position himself as a leader within the Shiite majority.
Previously, he tried quietly to get some distance between himself and Grand Ayatollah Sistani, whom he [and his now deceased father, killed in 1999] regarded as too moderate and apolitical. But with the car-bomb assassination of Ayatollah Al-Hakim late year, one of Sistanis main rivals is gone and Sistanis influence has stayed strong. Looking around, al-Sadr has realized that he cannot gain influence by speaking or apprearing to move against Sistani. Hence, the armed uprisings now: they show Sistani that he is not afraid of him while simultaneously offering Sistani a kind of alliance. According to the New York Times, al-Sadr just released this statement: "I proclaim my solidarity with Ali Sistani, and he should know that I am his military wing in Iraq... I will put the city with the golden dish [Najaf] between Ali Sistanis hands after liberation."
The key here is what Sistani will do. So far, he has tried to walk the thin line: urging calm but saying that al-Sadrs political demands for an end to occupation are not unreasonable. Since Sistani also cannot move against al-Sadr openly, the Coalition needs to destroy al-Sadrs armed force in such a way that impresses Sistani with our resolve but does not suggest that we are coming after him and the other Shiites too. A tricky business, but one critical for the transition.