The positions of most politicians on Iraq are either hoplessly naive or unspeakably hypocritical.
It is difficult to imagine any reason why a modest increase in troop strength (the Bush administration's surge) could make any meaningful difference. Perhaps an enorous increase might install some level of calm in the form of martial law. But this would merely suppress the political, ethnic, and religious divisions in the country temporarily; they would resurface whenever these trooops withdraw.
Similarly, it is difficult to see why any diplomatic approach or set of timetables and deadlines will work any better in the future than it has so far. The Iraqi government has neither the ability nor the desire to achieve the various transitional goals. Thus, this approach is just a way to shift blame from the U.S. to Iraq in preparation for eventual withdrawal.
So what options are left? Withdraw now. This approach has its own negatives; in particular, it might unleash a torrent of bloodshed. That outcome is not entirely pre-ordained; the Shiite majority might take control quickly enough that transition to a Shiite-dominated theocracy is less violent than the current situation. But a prolonged and deadly civil war is unquestionably possible.
But, whatever is going to happen is going to happen whether we withdraw tomorrow; or in a year; or in a decade. Our continued presence, if anything, only makes matters worse. So, we should just get out now.