This strikes me as in the neighborhood of being correct:
[Sen. Johnny]Isakson [R-GA], who had sat silent throughout the conversation with Frist, spoke up. ” I’m sorry, I can’t keep quiet on this,” he said. “The terrorists and those that are trying their best to attack us – and a lot of that is coming out of Iran – are concentrated on Baghdad. It’s a reflection of the success we’ve had in the majority of the country. If you confront that concentration now with the appropriate force and in conjunction with the Iraqi army and you can break its back, it has the chance to be a very optimistic result. If you turn the other way and say you’re failing, then you’ve handed them a victory. You have to remember the terrorists don’t have to beat us to win. All they have to have us do is quit and go home and they declare victory. You saw what Hezbollah did in South Lebanon.”
There are a couple of other hot spots, I think, but even Fallujah, as I recall, is peaceful now. One explanation for this may be that the religiously and/or ethnically relatively homogeneous places are relatively peaceful. And others may--fortunately or unfortunately, you be the judge--be sorting themselves out in that way, with some internal refugee flow.
But strategically it makes sense for all those who want the U.S. out and who want the Iraq experiment to fail to concentrate their efforts on Baghdad. Thats where the international press is. Thats the most target-rich environment. It cant be isolated or circumvented that way other enclaves can be. And a Baghdadi "failure" can relatively easily be billed as a general (U.S. and Iraqi) governmental "failure."