Obama's promise to pull out of Iraq immediately only makes sense if it is in the nation's best interest for us to pull out immediately. I'm not convinced that it is.
Building a nation from scratch is not easy...just look at our own history. It took more than a decade to work out all of our problems and inter-state bickering before we were able to write the Constitution and formulate a stable government.
With casualties at their lowest rate since the Iraq war began, progress is apparently being made... but attempts to resolve differences between Sunni and Shi-ite factions are still ongoing, and U.S. forces are needed to help further stabilize the situation and finish the rebuilding of Iraq's infrastructure.
As McCain and others have pointed out, exiting prematurely would dishearten our allies and encourage our enemies in the region. We need to finish the job, if for no other reason than to avoid both of those consequences....and to show the world that we finish what we start, and cannot be side-tracked by election year rhetoric.