One of the big culprits in the New Orleans floods was the degradation of wetlands south of New Orleans (story). The two big contibuting factors here are oil drilling in the swamp and the various levee projects that protect New Orleans from the Mississippi and keep shipping channels open.
The problem with the modern re-engineered delta is that the delta is a living system that requires replenishing silt from the Mississippi River to stay in tact. We can argue that the problem was man's interference with nature.
This argument falls apoart because, if left to its own devices, the Mississippi River would have changed course decades ago.
I contend that another big factor was the overall problems with the levee systems that came to light in the 1993 Mississippi floods. In this flood we found that the large number of levee projects in the Mississippi basin were increasing the magnitude of the floods. In the attempt to protect everyone from floods, the massive government funded levees were creating a situation where we were more at risk.
The 1993 flood really dampened the Federal Government's willingness to fund levee projects.
Added to this was the realization that federally funded levee projects had the strange tendency to encourage people to live in flood plains.
A wise nation would have doubled its efforts to protect major urban areas (St. Louis and New Orleans) and left the rest to major flooding. Sadly, we don't live in a world of wise government, we live in a world of politicians.
As for the political circus. Looks like we are starting the great finger pointing game. Fortunately, we see expresidents united in efforts to help in the clean up: This is the Bush Clinton Katrina Fund. Habitat for Humanity is gearing up for a major house building effort.