This is how it will end in Iraq, my assumption.
US won’t be forced out militarily, it will be asked to leave by the Shia and Kurdish government, and this will happen at a moment when US casualties become unacceptable, so it becomes some sort of half victory, we leave, but the government we helped foster is still standing, which is a marked difference from Vietnam (Obviously). Maliki won’t ask the US to leave, because he’ll be in his job for one term.
But what will be interesting is what will be left behind.
Now, back to some analogies on Vietnam, when the US withdrew ground troops, it didn’t remove air support. Now, air support is an ample way in helping a government struggling with insurgents by giving it the ability to have a tactical advantage over them which they don’t have. The US will do this, because one, it’ll shore up the government they helped set up to create, two, because it’s cheaper in lives and manpower to support and three, they don’t have to take responsibility for what happens on the ground, they can leave that to the Iraqi Government.
So what we’ll see is a marked reduction in the number of ground troops, and the increase of advisors and military contracts and supplies to the Iraqi security forces. So the US will withdraw, but never completely, and I don’t think Iraqi politicians want to see them gone completely either, since it benefits them both in terms of money and ability for them to retain their positions of influence.
The numerous theories of how the US would be cut off and supposedly stranded in Baghdad is implausable basically because if it were that easy, then Sadr who launched two uprisings, would of done it first, not to mention the numerous other insurgent organisations who can’t even pull it off. Also, just to mention, Hakim might be pro-Iranian, but he’s not stupid to cross the US. He’s also a considerable rival to Moqtada Al Sadr. Not to mention his organisation is much larger than his.
I see US withdrawal from frontline combat in about 3 years, if the current positions hold, however if not, I only see a marked reduction in US action and redeployment of forces to backing up the Iraqi security forces for the foreseeable future under the guise of advisors and financial support.