Bush probably told Nagin "either work with me, or get the hell out of the way." (only more politely). Nagin chose the latter.
Blanco chose to obstruct. She cares more about CYA than helping. Nagin may be incompetent, but I think his heart is in te right place.
Blanko's performance in this crisis foreshadows what Hillary's would be, were she president. These women are so insecure, that they would rather see everyone around them die than to admit their mistakes. I have seen this character flaw in the workplace, but in life-and-death situations the consequences are tragic.