Bush will be forced to resign over this. The death toll will be staggering, and the stories gruesome. But the real damage will come when all the FEMA incompetence is exposed.
Nixon and his advisors knew it was over months before the resignation, and the same thing is happening with Bush. The straw that will break him is the use of FEMA (and by extension Homeland Security) as a patronage system.
As with Nixon, someone from his own party will tell him it is over. Who will it be?