I was one of the first people saying this on the Katrina live threads last week - people were flaming me for being a tin-foil case. I think Blanco got a call from the DNC, telling her to "go easy" on maintaining civil order, because that would make the FEMA job harder, and therefore the relief efforts more difficult, which could be kicked back at Bush.
The more I see of Blanco, the more I believe she could not be THAT stupid, and therefore something else is going on. The Dems and the media instant assault on Bush looked pre-staged to me - they were ready in advance to launch it.