It's REALLY simple. Bush spent WAY less money than experts asked for to prevent hurricane destruction in the Gulf Coast. From today's Washington Post:
Louisiana's politicians have requested much more money for New Orleans hurricane protection than the Bush administration has proposed or Congress has provided. In the last budget bill, Louisiana's delegation requested $27.1 million for shoring up levees around Lake Pontchartrain, the full amount the Corps had declared as its "project capability." Bush suggested $3.9 million, and Congress agreed to spend $5.7 million.
Administration officials also dramatically scaled back a long-term project to restore Louisiana's disappearing coastal marshes, which once provided a measure of natural hurricane protection for New Orleans. They ordered the Corps to stop work on a $14 billion plan, and devise a $2 billion plan instead.