CW says that if Bush pulls U.S. forces out early (by early I mean down to 30 - 50,000 troops by summer) chaos and civil war will ensue. I doubt that.
There are three centers of gravity in Iraq who have all played the post Saddam world in different ways. Both the Kurds and the Shi'a have patiently maintained (and increased) their large capable military forces while the Sunni insurgency has been smashing itself against the power of the U.S. military for some time. For more detail analysis on the Iraqi power centers read: Link
The irony is that the only thing protecting the Sunni people right now are those same U.S. forces. How long do you think Bush will play protector to the same people that are attacking us? Remove that force and instead of the power vacuum CW predicts, you have two powerful elements strategically aligned against the third. Here's what happens next...
The most likely outcome of the elections is Shi'a domination at the polls. After a brief transition to consolidate power they will ask the U.S. to pull back to their bases and start drawing down. The Shi'a and the Kurds will then quickly and ruthlessly dominate the Sunni with the Kurds taking Kirkuk and the Shi'a controlling Baghdad. From Bush's perspective this will be an acceptable outcome since he can claim the new Iraqi government was freely elected and that the Shi'a and Kurds are standing up to protect their own country. They will crush the Sunni insurgency using the Saddam like tactics that were used against them.
The big question from this outcome is how it impacts U.S. interests. From a neo-con perspective you have to think they would be happy as long as the U.S. were able to maintain some modest basing rights. Why would a new Iraqi government allow U.S. forces to stay? This is a classic case where divergent groups' self interests align. For the American conservative hawks a much smaller contingent of U.S. forces confined to their bases could retain a foothold in the region for threatening Iran, Syria or Saudi Arabia. For the new Shi'a Iraqi government our troops provide protection from its external threats. These threats are primarily from Turkey (which is the biggest wild card), Saudi/Syria Sunni interference and Iran.
The unanswered question regarding Iran is the level of influence they will have within the new Shi'a government. I suspect that while there are friendly ties, the Iraqi Shi'a would welcome the U.S. protection in order to maintain their independence. Historically the Persian and Arab Shi'a have been friendly but not united. This may just pass as regional stability in the short term.
Domestically this plays well for Bush. The anti-war left and growing U.S. middle gets the withdrawal of U.S. troops that it wants. The hawks get to re-build the U.S military while keeping their fingers in the oil pie without having to turn to the hated U.N. or "old Europe" allies. Bush will spin this all in "Bush-speak" as a victory over tyranny and the triumph of freedom and democracy.
The real test is if this outcome produces enough stability and reform in the region to justify the U.S invasion with its huge cost in lives, dollars and credibility. I doubt it.