*The United States cannot determine political outcomes or achieve its remaining political aims via military means. American military forces have not brought the violence to an end or under control and will not do so in the future. In the absence of the understanding and the intelligence needed to operate effectively in the complex and violent political situation in Iraq, this should not be surprising.

*Leaving U.S. forces in Iraq under today's circumstances means the United States is culpable but not capable -- that is, Washington bears substantial responsibility for developments within Iraq without the ability to shape those developments in a positive direction. In consequence, Iraqi support for the U.S. presence has collapsed. Polls indicate that most Iraqis want the United States to pull out. Moreover, the Iraq war has fueled the jihad and apparently been a godsend to jihadi recruiters—and the process of self-recruitment -- as indicated by the 2006 National Intelligence Estimate (NIE) on the global war on terror. More broadly, the Iraq war has had a very damaging effect on the U.S. reputation in the Arab and wider Islamic world. Authoritative opinion surveys show this as well. The continued presence of U.S. forces is thus a severe setback in the canonical war of ideas, which the Bush administration has correctly assessed as crucial to American interests.

*The ongoing war has empowered and advanced the interests of the chief U.S. rival in the region, Iran. At this stage, the best way to regulate Iran's attempts to exploit its advantages is to negotiate with Tehran either bilaterally or in a multilateral framework while protecting Americans in Iraq against Iranian attack.

*By siphoning resources and political attention away from Afghanistan, a continuing military commitment to Iraq may lead to two U.S. losses in southwest Asia.

*The Iraq war constrains the U.S. military, making it very difficult if not impossible to handle another significant contingency involving ground forces. It also damages the U.S. military, making it difficult for Washington to credibly employ coercive policies against others in the near to medium term even once the United States has disengaged from Iraq. Furthermore, the military commitment in Iraq impedes the U.S. ability to address other important international contingencies, in part because of the limitations of the U.S. military but also because of the preoccupation with Iraq at the highest decision-making levels. In short, U.S. interests in the Middle East and Persian Gulf region can be more effectively advanced if the United States disengages from Iraq. Indeed, the sooner Washington grasps this nettle, the sooner it can begin to repair the damage that has been done to America's international position. Staying longer means more damage and a later start on repair.

*The implosion of domestic support for the war will compel the disengagement of U.S. forces; it is now just a matter of time. Better to withdraw as a coherent and at least somewhat volitional act than withdraw later in hectic response to public opposition to the war in the United States or to a series of unexpectedly sharp reverses on the ground in Iraq.

With 4,000 to 5,000 increasingly sophisticated surface-to-air missiles in the hands of insurgents via the international arms markets, analysts say, American chopper pilots are caught in a narrowing flight envelope in which they can operate with relative safety. It takes years for the Pentagon to develop and field new defensive technology such as infrared jammers.

Each wrenching loss of a helicopter and crew brings an official statement saying that the military is studying new tactics. But this style of warfare requires that helicopters operate over mostly hostile territory, and pilots say there are precious few tactics that haven't been tried before.