Such a relatively small, tailored force would not be big enough to wage a war, but it might be enough to deter a new one from breaking out. An Iraqi civil war would likely be a three- or four-sided affair, with the Shiites breaking into pro- and anti-Iranian factions. It could also easily metastasize into a regional war. Neighboring powers like Turkey and Iran are already involved in Iraqi affairs, and the Sunni Arab states would be unlikely to stand by and watch a Shiite-dominated regime in Baghdad slaughter the Sunni minority. A regional war in the middle of the world’s oil patch could shake the global economy to its foundations and make the current recession look mild.

In addition, a continued American military presence could help Iraq move forward politically. No one there particularly likes having the Americans around, but many groups seem to trust the Americans as honest brokers. And there would be a moral, humanitarian and political benefit: Having American soldiers accompany Iraqi units may improve the behavior of Iraqi forces, discouraging relapses to Saddam Hussein-era abuses, or the use of force for private ends and feuds. Advisers not only instruct Iraqi commanders, they also monitor them.