This says it all and it would be an injustice to even attempt to summarize his great writeup. But I will include his closing paragraphs:
So: A crony with no relevant experience was installed as head of FEMA. Mitigation budgets for New Orleans were slashed even though it was known to be one of the top three risks in the country. FEMA was deliberately downsized as part of the Bush administration's conservative agenda to reduce the role of government. After DHS was created, FEMA's preparation and planning functions were taken away.
Actions have consequences. No one could predict that a hurricane the size of Katrina would hit this year, but the slow federal response when it did happen was no accident. It was the result of four years of deliberate Republican policy and budget choices that favor ideology and partisan loyalty at the expense of operational competence. It's the Bush administration in a nutshell.
Please go read the details. I didn't vote for him.