Military gunships cannot operate within any city in the United States of America unless the Governor of a state declares Martial Law.
Despite the rumors that martial law has been declared, Secretary Chertoff made it clear that Governor Blanco has not done so.
The military can assist with rescue, but they cannot operate with law enforcement to quell unrest. Unfortunately.
So this become a federal issue, who CAN issue Martial Law in a specific area during a national emergency.
I would suspect this is one of the reasons why Congresss needs to be there in 24 hours.
George Wallace thought the U.S. military couldn't intervene in Alabama either. He found out otherwise.