Any answers yet?
Someone I know emailed me from Baton Rouge (a lawyer), after he got up there; he told me Nagin was a professional who had a good job and sweet salary, gave it up to be mayor (not much money and had to switch parties to do it). He said he has no expertise in the job but he was a good guy (and a party animal)... and said there was more to the story
I have a gut feeling that there IS a lot more to the story - that his inaction was the "action" he was supposed to take, and that his hurried meetings in Dallas had something to do with it.