Obviously, we need to go back.
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How many troops and for how long? What precisely is the mission? How will we accomplish building a nation this time? How will the US fix the Sunni - Shiite issue? The Kurds?
You raise many important questions. Each of the answers will involve a concept that includes our continuing presence and some degree of restructuring, just as was required in Japan and Germany after WWII. Otherwise, as we can see today in Anbar province, we almost certainly will be unable to effectively correct the problem.
You and I no doubt agree that we should never sacrifice American lives piecemeal for no more than a short-term and obviously incomplete solution and then expect the problem to correct itself.
Sarcasm, but it’s what I’m hearing from a few talking heads. Obviously, neither they nor their children will be going, and it’s all on the national credit card, so why not?