Citing this Newsweek piece on the ethnic cleansing that's ongoing even during the "surge," both Kevin Drum and Matt suggest that, in Matt's words, "it's worth considering the possibility that the essential 'plan' in Iraq is just to stay there, in force, vaguely allied with whichever side (or sides) we perceive to be willing to ally with us, until, eventually, the civil war ends, a brilliant victory is portrayed, and the hippie peacenik scum are told to beat it. After all, civil wars do end if you just wait long enough."
Take out the sneering and yes, this is the case for staying in Iraq that seems most persuasive to me at the moment. By remaining there in force, this argument runs, the U.S. can mitigate the violence associated with ethnic cleansing, degrade al Qaeda's capabilities, and prevent the bloodletting from spreading beyond Iraq's borders - with the long-term goal of ensuring that the civil war burns itself out with as few civilian casualties and as little collateral damage to U.S. interests in the region as possible. The hope would be that Iraq eventually settles into a relatively stable state of de facto partition, with a weak central government and strong regional power centers, and with the various fault lines policed by a much-reduced American force. And were this goal achieved you would declare victory, not to stick it to the hippies but because that's what you would have won - not the victory we hoped for in 2003, certainly, and the not the kind of victory that lends itself to Gettysburg analogies, but victory of a certain kind nonetheless.
Now it may be that the American presence in Iraq, far from mitigating the violence, is actually making it worse (by effectively funneling arms to sectarian militias, etc. etc.). And it may be, as Matt says, that the civil war could take decades rather than years to burn itself out. Both of these possibilities, along with the ongoing loss of life, the cost of the occupation, and so forth, militate against the "stay till it burns itself out" strategy. But given that most of the plans for phased withdrawal that I've seen run the risk of ending up as a more-ineffectual variant of exactly the same strategy we're employing now - with a much-reduced U.S. presence trying to, well, fight al Qaeda and mitigate the ongoing violence - it's hard for me to dismiss the idea that staying in strength might be the lesser of two evils.
Update: I should note that this Hilzoy post, despite some fuzzy math in the title, is the most comprehensive rebuttal I've seen to the "stay till it burns out" point of view.
U.S. Navy photo by Mass Communication Specialist 2nd Class Scott Taylor.