I think as Democrats we need to start developing a better view of what is on the horizon in Iraq and forming a party policy that will somewhat reflect the real realities that will face us in the coming elections. Many think we should declare victory and pull out like we did in Vietnam. Unfortunately, from a strategic political view I don't think we are afforded that option. In vietnam we could leave because there was no real strategic interest for us to be there beyond the notion of the "domino theory" and being tough on communism. In Iraq we must stay and see this out because unfortunately we need the oil and we need to maintain stability for our partners in the Middle East (i.e. Turkey, Jordan, Kuwait, Saudi Arabia)
Access to oil is becoming and will become even more important in the future. Hence why we have high gas prices. "he who controls the oil, makes the rules" is the new strategic mantra of the 21st century.
With that said here are some possible Scenerios that I think may happen.
Sistani dies, the shiite cleric who has been instrumental in tempering shiite violence against Americans and Sunnis. If he dies I would expect to see a full fledged Sunni Shiite civil war within months.
Constitution fails and the Iraqi people become fed up with the gov't and start vying for independant shiite, sunni, and kurd countries with military actions between all three for territory and wealth.
an Iranian backed Shiite gov't becomes a hard line gov't and becomes overly oppresive in attempt to bring the insurgency to its knees. Which will force the US to ironically start supporting sunni insurgents and kurds.
All The scenarios I have pointed out I think will inevitably end up with three separte autonomous regions with major state backers. Similar to the conflicts that arose in the Balkans during the 90's. In any event I don't see how US troops could leave without such conflicts spilling over into countries that are vitally important to us or without signaling to the rest of the world that we are taking a back seat to global politics in the future.
I'm not expert but this is what I come up with and I think as a party that wants to regain Americans confidence in foreign policy we need to develop a coherant plan of how we're going to maintain American interest and reduce troop levels.