What to do now? Well, to paraphrase Colin Powell, "we broke it, we bought it". So I suppose there is naught else to do but prop up some semblance of a government, leave, and hope for the best.
9/11 happened while the middle-east was far more stable than it is today. Piling more American lives upon the pyre will do litle to prevent a repeat, I suppose.
The job is not only to prevent a repeat...its to prevent a nuclearized repeat. In that effort Iran is the key target...and Iraq is a very strategic location in the goal of remaking, or removing, Iran.
By all measures, each American lost in Iraq is a huge loss - but the total numbers are low when compared to other wars. We lost 870 last calender year. We lost 470 to gunfire in Philadelphia in the same time period. Thats in only one US city! I was around (but not old enough to fight) on D-Day and Iwo Jima. Check those out by way of comparison. American's were willing to sacrifice to keep fascism at bay then....and Militant Islam is every bit as Fascist (if not more so) than the Nazi's.
Thank God for the brave of America.
Then perhaps stability in the Middle East isn't what we want. Perhaps we are better off when they are unstable and snapping at each other like dogs.