Nonetheless, we need some central government. The Iraqi state may be a shell but it is a necessary one because de jure partition into separate states would invite military intervention by the neighbors -- Turkey, Iran, Saudi Arabia and Syria.

A weak, partitioned Iraq is not the best outcome. We had hoped for much more. Our original objective was a democratic and unified post-Saddam Iraq. But it has turned out to be a bridge too far. We tried to give the Iraqis a republic, but their leaders turned out to be, tragically, too driven by sectarian sentiment, by an absence of national identity and by the habits of suspicion and maneuver cultivated during decades in the underground of Saddam's totalitarian state.

All this was exacerbated by post-invasion U.S. strategic errors (most importantly, eschewing a heavy footprint, not forcibly suppressing the early looting, and letting Moqtada al-Sadr escape with his life in August 2004) and by al-Qaeda's barbarous bombing campaign designed explicitly to kindle sectarian strife.

Whatever the reasons, we now have to look for the second-best outcome. A democratic unified Iraq might someday emerge. Perhaps today's ground-up reconciliation in the provinces will translate into tomorrow's ground-up national reconciliation. Possible, but highly doubtful. What is far more certain is what we are getting now: ground-up partition.

Joe Biden, Peter Galbraith, Leslie Gelb and many other thoughtful scholars and politicians have long been calling for partition. The problem is how to make it happen. Top-down partition by some new constitutional arrangement ratified on parchment is swell, but how does that get enforced any more than the other constitutional dreams that were supposed to have come about in Iraq?

What's happening today on the ground is not geographical line-drawing, colonial style. We do not have a Mr. Sykes and a Mr. Picot sitting down to a map of Mesopotamia in a World War I carving exercise. The lines today are being drawn organically by self-identified communities and tribes. Which makes the new arrangement more likely to last.

This is not the best outcome, but it is far better than the savage and dangerous dictatorship we overthrew. And infinitely better than what will follow if we give up in mid-surge and withdraw -- and allow the partitioning of Iraq to dissolve into chaos.