As mentioned, the Presence of US troops is one of many factors causing the problems in Iraq. IMO, they are part of the problem, not part of the solution.

We can not sit in the middle and prevent a civil war, and if US troops are the only thing stopping one, then we have a big problem unless we want to occupy Iraq for decades like Israel has occupied palestine. Our "victories" we have had could also be had by the Iraqi government. For example this new "Al Qeada Deputy" that was captured and touted by the right wing was captured from a tip off. Like the Iraqi's couldn't go in and get him too.

When the US Troops leave, the Iraqi people will realize that they are in their own boat and will make it what they want, which is the only way Iraq will succeed. And if when we leave, a civil war breaks out, then we need to support the democratic government with money and weapons. If a taliban regime does somehow gain power, this is a worst case scenario and we would then need to take a couple of days and take the country back again. But having US troop presence is obviously not detering anything.