There you go! It's possible he couldn't. We have made progress! You will find that more people will want to continue to help hash this out if you are willing to admit that we just don't know that right now.
There is absolutely nothing that I can find showing that the IA has ever been invoked in a natural disaster. Nothing. I've looked, off and on, and found nothing. Hopefully someone will have better luck than me.
The impression I am getting is that it has never been done before. It has never ever had to have been invoked in direct opposition to the governor of a state. And that's why it took some time. Legalities did have to be argued out; Bush could not do something without a clear legal precedence. It is possible that had Bush not been so proactive in trying to find a way to get around Blanco, federal troops would still not be in New Orleans. That's why I'm not outraged YET at the delay for federal troops to show up.
I am outraged at the mayor and governor, because their culpability is clear. For the head of the Red Cross to go on national television and state that the state officials said not to bring food and water because they didn't want people to stay at the superdome, the guilt of those officials is clear. For Blanco to resist help when she so clearly needed it, her guilt is clear. Every death that occured because she withheld food and water, every death that occured because she would not accept help, she has total or partial guilt. Now later, if it is proven that Bush had the authority to invoke the IA on Wednesday afternoon, after things kind of settled down, then I will gladly, happily settle guilt on him, too.