It is seldom done, but the specifics of this event make it worthy of a seldom used plan. Bush just needed to have a plan to use the full resources of the federal government once it was clear a Cat 5 was about to strike the Gulf, with the obvious consequences of such an event, call Nagin, Blanco and Barbour and tell them of his intention to take this problem off their plate, and give a speech to the nation once it hit declaring that the elected officials have been notified of the plan and are on board and that the federal government would be mobilizing its available resources to fight this national security crisis. The National Weather Service issued a release Sunday morning detailing in perfect detail what was about to happen to NOLA in what was probably seen by many Average Joes as hysterical Hollywood-esque hype, so the feds were certainly aware of what that area would look like after the strike by Katrina.
Among many things in your posts that are wrong is the fact that this storm did not hit as a CAT 5.
These storms give a two or three day warning, and the tracking is very accurate now. Much can be done if there is preplaning, pre-positioned military staging areas and intensity and focus. We are in the decade of intense hurricanes, and strong hurricanes are likely to hit again and again, and when they hit the shallow waters of the gulf, huge storm surges will hit again and again.
So suppose President Bush shoved Nagin and Blanco aside before the hurricane (before it was evident how criminally incompetent they were) "took over" and sent in the National Guard. Do you really think this nation would have stood for this? (Remember, this is BEFORE the hurricane hit.) That is the stuff of dictatorship.
It may be onerous to have to defend the President's actions to all the ignorant masses who think he should have intervened earlier, but President Bush is not pre-War in Iraq Saddam Hussein and does not have unlimited powers!