If the US military, in alliance with factions in Iraq hostile to the Sadrist current, continue to push too hard, they will force a response from Sadr - either of his own accord or as a result of mounting pressure from an increasingly hawkish Sadrist leadership. That would not be good.
Update by Cernig How the US military is likely to react to Sadr's militia has, however, been strongly infuenced by his ceasefire. We've noted here before how Petraeus has been talking to senior Sadr aides behind the scenes and how he's instructed his officers to use respecteful forms of address when talking about Sadr. In that regard, I think this excerpt from a London Times interview with Petraeus yesterday is instructive:
The reason for the ceasefire was to enable the leadership of the movement to get a grip on individuals who had tarnished the reputation of the movement by their actions in Karbala, in assassinating two southern Governors and police chiefs, kidnapping Government officials and a journalist in Basra most recently, who was there to meet with the Sadrists officially. This is a movement that was built on the principles of the martyr Sadr, Moqtada’s father, and it was all about serving the people not extorting money from them, carrying out criminal actions against them. I think that the leadership of the movement is concerned that some of these individuals have again carried out activities that are clearly blemishes on the reputation on that movement. As they approach elections and so forth that is a big concern to them. We think that the intellectually logical move would be to continue the ceasefire, to continue to try to clean up the organisation, to deal with the rogue members in it and to try to get back to the principles that attracted the Iraqi people to it in the first place.Petraeus there definitely sticking to the Sadrist line, rather than the old "one of the biggest threats" narrative that was previously popular.