Success in Iraq was never certain. It depended, in part, on the amount of effort Americans were willing to exert in the endeavor, but also on a number of factors beyond U.S. control. War advocates never seriously contemplated the price; they merely asserted on the eve of war that the costs of inaction outweighed the costs of action.
For a time, the American public went along. Six years later, a solid majority disagrees. In poll after poll, Americans say the costs already paid far exceed whatever benefit will be derived from the war.
If America itself were threatened by the possibility of renewed large-scale violence in Iraq, there would be no discussion: The U.S. would simply invest what was necessary. But Iraq always was, and still is, a war of choice. The U.S. should choose to terminate the mission and refocus its attention — and, where appropriate, its still-strong military — on the enemies who struck on 9/11.
That the choice is clear does not mean the choice is easy. The consequences of a U.S. withdrawal may be difficult, particularly if political reconciliation collapses and there is renewed civil war. But as it stands now, it is American personnel — troops and diplomats, and also private contractors — who are exposed to these risks. The time has long since come for the burden to shift to the Iraqis.