Fighting al-Sadr

I keep wondering about this and keep not seeing any reporting on it, but when, exactly, did we make the policy shift that the United States is at war with Muqtada al-Sadr's militia again? As you'll recall, there was a period when we weren't fighting his forced. Then there was a period when we were fighting his forces. Then there was a settlement and we weren't fighting. Then his political party participated in the elections and even took seats in the Iraqi cabinet. But now we, along with Iraqi government troops, are fighting him again. When did this happen? And why? I'm not criticizing, per se, but I'd like to know what's going on and I'd think people would be more interested in this sort of subject. Instead, you still hear talk about "succeeding" or "failing" in Iraq but it's not obvious what the administration is even trying to do.