Maybe I can quickly answer that one. One of the challenges was that those whom the feds would normally help were no longer available. By and large, a lot of the first responders were dead or gone. So you didn't have a state asking to assist its first responders, because the first responders were no longer there to ask for assistance.
No one had planned and practised that kind of event. The U.S. government is now taking a look at whether federally they would impose their assistance on a local jurisdiction if they saw this happen again. That is something they are dealing with.