McCain needed an awful emergency in NO to look like he was where he was needed. (Don't ask me for what.)
Now Gustav is a wimp. But, will the levees hold? If not, there will be no great loss of life. McCain will, of course, say that this is a result of prior planning.
So why didn't they plan properly for Katrina? And, if the levees fail again, how well did the government learn the lessons of Katrina.
Mere gale-force winds and a Cat 5 flood would be an embarrassing calculation to explain.