Of the objectives for going to war in Iraq, all have been accomplished, leaving only two. First, to leverage the war and the regime change as a positive influence and force for change in the region. Second, to liberate the people of Iraq and help them achieve both peace and freedom.
There are three ways that the first objective could be accomplished – (1) by retaining a significant military presence in Iraq indefinitely; (2) by assisting the Iraqi government in achieving stable, functional, America-friendly government with orderly succession and a no more than tolerable level of violence; or (3) complete military withdrawal following the completion of major military operations and the capture of Saddam. The deadline for (3) is past – any withdrawal now or in the future which does not leave behind a stable, functional, America-friendly Iraqi government will appear to demonstrate that the US military and US policy have been defeated, with the resultant failure of this objective.
The second goal is humanitarian and stems from values-based policy rather than national interest. It may be argued that as the Iraq war has caused havoc and change for the Iraqi people as a side effect of the accomplishment of goals of US national interest, the US government owes the Iraqi people a debt which can only truly be discharged by assisting them in their struggle to achieve a free and peaceful society. This of course presupposes that the majority of Iraqis desires a free and peaceful society, but it appears that most do. This objective could only have been achieved by ways (1) and (2) above – way (3) would have left the Iraqis to pick up the pieces by themselves, or perhaps with the assistance of humanitarian agencies.
Ways (1) and (2) both require of the US government a significant military commitment, and more than that, a significant commitment of will, that is, a willingness to do the hard yards and stay for a medium to long term, a minimum of 2 more years and probably rather more.
The question is whether the US government, and the US electorate, considers either way (1) or (2) to be worth the trouble. Either way will mean more blood and treasure expended for no obvious or short-term gain. Quitting on efforts to achieve the first goal will mean bigger problems for the US and its allies in the future, though how big and how far away is debatable, and democracies are notoriously short-sighted in their forward planning. Quitting on efforts to achieve the second goal will just mean lots of dead and maimed Iraqis, as well as a domestic Iraqi outcome that will be determined by whichever group emerges as the strongest and most ruthless combatant.
With specific regard to the use of withdrawal, whether phased or set to a timetable or all at once, as a stimulus to Iraqi officials and institutions to become more capable, I rather suspect that such an ominous development would instead result in an exodus from Iraq of many, perhaps most, of the Iraqis who hold office or administer institutions, along with their families and assets. What would remain would be those who would rather fight, those who would rather die, those who lack the resources to flee, and those who hope it will all somehow turn out all right.