Nagin was a Republican once I believe, and I don't think he and Blanco ever got along. I would think the DUmmies will support Blanco more than Nagin, and especially if Nagin said what he did about Blanco, they'll turn on him.
Nagin endorsed Jindal in the governor's race over Blanco. That would seem to confirm what you said about them not ever getting along - she probably is holding a grudge against him as well.