They really don't want to investigate Katrina. It won't serve the Dems at all to focus attention on something that's already been placed at Pub feet in the popular mind, but in reality is spread pretty evenly between the two parties. There's nothing to gain and quite a bit to lose.
Will they include the part about Jesse Jackson screaming "RACISM!!!" when FEMA tried to Wargame a hurricane hitting a large city, with social unrest as one of the results??
Welfare minorities would NEVER riot when all the social services and Police protections break down, would they?