The War Nerd offers his thoughts.
But he misses one possible solution to the current insurgency. If the guerillas wind up scaring off all of our allies in the Sunni Arab regions, the US always has the option of simply considering all Sunni Arabs the enemy.
No, I'm not advocating this; but I think that if the US has its back to the wall, sooner or later it will be decided that increased brutality to the Sunnis will force them to submit. And if regular brutality doesn't work, perhaps razing villages to the ground, punishing the families of insurgents, or concentration camps for the Sunni Arabs will be used.
But one thing is clear: there is no pretty, happy solution to the Iraq War. We either leave and let whatever happens happen, or we stay, hemorrhaging troops in a growing insurgency, or we decide to show the Iraqis that anyone who doesn't play ball like we want them to will die, and a lot of bystanders too, just to encourage them to listen.
Personally, I like the pull-out option, but I have a feeling that in the end, Iraqi lives will be considered the most expendable thing here.
That is all.