They've had decades to work on improving those (long before Bush was president) and haven't done anything about it. In those 40 years or so since the last big one hit there, they obviously haven't done anything to really protect the area. You can't lay that at Bush's feet. Maybe he did cut funding to FEMA, but that didn't stop them from doing something before that happened.
You can't single out Bush for exhibiting the same cavalier disregard for dire warnings from engineers and scientists that politicians always have; the film "Jaws" mocked this particular mental failing of politicians some 30 years ago. As long as we prefer lawyers and salesmen over scientists and engineers for national leaders, this kind of thing will continue happening.
However, you can
single him out for basing his entire political campaign for the last 4 years upon "protecting" the people, and then finding out the hard way that apart from attacking Iraq, he really didn't do anything about national security. When a man sells you something based solely on the notion that it keeps you safe, you have a right to get upset when it fails to perform as advertised. And the fact that Haliburton is grabbing up a lot of the Katrina rebuilding contracts from the government is going to leave a sour taste in peoples' mouths too.