I don't think total, complete withdrawl was ever our intention. I expect in the back of the Pentagon's mind was the hope we would end up with a situation like Germany and Japan, where we had "strategic interests" for decades. A jumping off point would be highly valuable in the region, especially since things didn't go so well in Saudi Arabia.
That said, the only way we can do that safely is to crush the insurgency, and until the Iraqi people are tired of seeing their peers blown up we can't. It's a supreme lack of sympathy on their part that is the problem. The people who hide al qaeda don't mind seeing people in other areas blown up. Baathists don't mind seeing shiite mosques attacked. The shiites don't mind the US wreaking havoc in sunni areas.
If the people harboring these terrorists would one day look at the carnage after a bombing, and say "I don't care if I personally don't like those people, this has to stop", the insurgency would be over. The places these people live have neighbors who know they are there. Those neighbors have neighbors. Until Iraqis align themselves with Iraq as a whole instead of terrorists and subgroups, this won't end.
I'm afraid that there is a lot of dirty work to be done, frankly. I expect when we leave for there to be a Stalinesque "purge" that will either cement the new government or destroy it. Put simply there are people in Iraq that will not tolerate peace under these terms, and until they are somehow convinced or purged from the society, there won't be peace.
That said, you can have a stable nation without it. Israel has withstood these kinds of attacks for years without the need of a occupying force. I don't think we can be out in six months, but I don't think the next President will be managing their affairs. Expect a strategic base to be eventually set up, probably in Northern Iraq, and for our forces to be use it for many years to come, though.