Good piece by Matt Duss. I especially like the last bit:
Perhaps most importantly, no real consensus yet exists among Iraqis as to what the new Iraq will be. Consensus does exist, however, around the belief that no genuine, sustainable Iraqi unity can develop while the Iraqi government continues to be underwritten by a foreign military presence. Recognising the latter consensus is essential for enabling Iraqis to arrive at the former.
This is important. To say that we can't leave Iraq until we succeed, or else that we can only now contemplate leaving Iraq because we've succeeded (because "the surge worked" or what have you) is to miss the point. The underlying problem in Iraq has long been the lack of any kind of consensus over what a legitimate Iraqi state would look like. But one point on which there is something resembling consensus is that a legitimate Iraqi state can't be permanently in a state of American military occupation.