The Iraqi government refused to deal with Sadr after the fall of Saddam, when he was just another small time religious thug with a small following. The US pressed the Iraqi's to arrest him for involvement in various sectarian murders, and they refused. After the US is out of the way the current leaders will either have to cut a deal with him, and/or be assassinated themselves. Not exactly a novel political concept in the Middle East.

I don't want the US to be involved in any assassinations, but then wish in one hand spit in the other, see which one fill up fastest.