For all the arguing I've done with Rabbi on this point, I guess I basically agree with him. If we changed our tactics and overall strategy and resolved to stick this out for the ten years that insurgencies typically take, we could bring this to a positive conclusion.
But that would require both changing our tactics and overall strategy and finding the national resolve for the long ten-year slog.
There are several reasons why this is unlikely. The primary reason is that our leaders seem unable to change tactics or develop a sensible strategy. They seem unable to even identify the true nature of the conflict. When we were faced with an insurgency, the Administration denied its own eyes and refused to admit we were facing an insurgency. When we were faced with a low-grade civil war, they refused to acknowledge that fact. They had just barely admitted that we were facing an insurgency by that time. Now that we are on the verge of realizing we are facing a low-grade civil war, that civil war is threatening to erupt into a regional war, with the Saudis and Iran getting into the fight. If the administration continues with this disasterous pattern, by the time they realize that we are in a regional war, world war may have erupted.
There are other problems besides the delusional nature of our leadership. As mentioned above, we are at a point where the insurgency has become a civil war. This is a very different animal. Civil wars burn much brighter and faster than insurgencies and tend to be much bloodier. These characteristics will make the second part of the equation--rousing national support for an extended military occupation--much more difficult, if not impossible. Remember, the Soviet Union was unable to generate enough national support to maintain its troop presence in Afghanistan, and the USSR was a totalitarian state. Imagine how much more difficult the task of rousing support would have been in a democratic republic like ours.