Tuesday morning, it should have been obvious that this went from a minor emergency to an absolute disaster. Anyone who knew anything about New Orleans, and all the media attention before the hurricane about the worries that it would break the levees knew what would happen if they broke. From the instant that happened, getting the national guard and resources out there, evacuating everyone out of there possible should have become a top priority.
Heck, I saw that news, and the graphic of the shape of New Orleans (the infamous bowl), and knew right there that the city was probably lost. It's shocking, and I can see shock and disbelief working for a little while, but there are plenty of disaster experts accessible and probably working for the government at all levels (federal, state, city) to tell what that meant.
Right at that point, everything should have been going in high gear.
FEMA ticks me off - keeping needed supplies out - I get the feeling they were a little territorial on the disaster - but since they didn't have the situation handled, they should have been welcoming help, not blockading it. Doubly so when they allowed the media in!