The United States has two options in Iraq: stay and try to win, or cut, run, and lose. Attempts to chart a middle course--partial withdrawal or redeployment, accelerated hand-over to the Iraqis, political deals with Syria or Iran--ignore the realities of the military situation. The real choice we face is this: Is it better to accept defeat than to endure the pain of trying to succeed?
The U.S. military, under the stewardship of CENTCOM Commander General John Abizaid, has worked hard from the outset to avoid creating an Iraqi military that is dependent upon the continued presence of U.S. forces. The fear of such dependency is one of the pillars that has supported U.S. strategy from the outset. In order to avoid it, the U.S. military has never fully committed to conducting coherent and comprehensive counterinsurgency operations on its own, preferring to wait until the Iraqis are able to undertake them. We are still waiting, and the insurgency is strengthening its organization and inciting chaos through mass murder and sectarian violence.
The Iraqi military, unfortunately, is still a work in progress. Although there are growing numbers of trained Iraqi soldiers formed into increasingly competent tactical units, those units remain highly dependent on American logistical support for food, shelter, ammunition, and transportation. This situation is not entirely the fault of the American military. It stems also from the failure of the Iraqi government to establish ministries capable of performing their assigned tasks--a failure abetted by woefully inadequate assistance from the nonmilitary agencies of the U.S. government. Abizaid and the U.S. military are right to feel let down in this regard by the rest of the government, but only partly. Their failure to establish reasonable security and safe working conditions in Iraq, particularly outside the Green Zone, where much of this effort would have to take place, is the principal cause for the lack of economic and political development.
Wherever the blame for this failure lies, there is no denying that it has occurred. The Iraqi military cannot function without a significant American logistical presence. It cannot continue to improve in quality without a significant American training presence, which includes a partnership between Iraqi combat units and coalition combat units conducting counterinsurgency operations. These facts make nonsense of any idea of significantly reducing the American presence as a way to "incentivize" the Iraqi military. Redeployment on any significant scale will not incentivize the Iraqi military. It will lead to its collapse.
Consider the current deployment. There are now about 150,000 U.S. service members in Iraq, including perhaps 65,000 in 16 brigade or regimental combat teams (the troops who regularly conduct raids, patrols, cordons-and-searches, and so on). There are also about 5,000 soldiers permanently engaged in training Iraqi units. Most of the remaining soldiers are primarily engaged in supporting these efforts and the survival of the Iraqi army. They maintain supply depots and supply lines. They transport essential goods around the country and distribute them at FOBs (forward operating bases). They keep both the U.S. and the Iraqi armies alive and moving. They are assisted by numerous civilian contractors and even local Iraqis, but the military personnel provide the glue that holds the entire effort together.
"Redeployment" of U.S. forces would therefore have to be quite modest. Perhaps 35,000-40,000 support troops would have to remain if the 130,000 soldiers in the Iraqi army are to keep functioning. Most advocates of "redeployment" propose increasing the training effort--surely a precondition of success in such a scenario--by 5,000 or even 10,000 soldiers. That would mean a minimum presence of at least 50,000 troops. Security for the Green Zone, which would still contain a vast embassy and essential command headquarters, would require at least another couple of brigades, say 5,000-10,000 troops. Lines of communication from Kuwait to the FOBs would require a few more. We'd also need to retain at least a brigade and probably two in ready reserve, since the new military posture would be entirely defensive and reactive. It's hard to imagine how fewer than 70,000-80,000 soldiers could suffice to maintain the barest functionality of the Iraqi army, even without conducting any counterinsurgency operations of their own.