Leonie, I don't think that the US was short of soldiers on its own soil in the aftermath of Katrina. I do not believe that there will ever be a lack of soldiers on US soil in the case of a terrorist attack.
The biggest issue is the delay of response. I don't believe the soldiers were particularly well versed in mass flood rescue either, or at any rate not as the Dutch military might be.
In terms of a terrorist attack, a great deal of the ground work is done by the police, ambulance and fire/rescue services. This is assuming that a terrorist attack would be in the form of explosions and hijacks. As a direct response to a terrorist attack, the military is pretty useless except for additional manpower and policing. Unless martial law is declared.
The military response to a terrorist attack would be action overseas, with counter terrorism units (which there are many) to do their job. Counter terrorism units are designed for extremely quick response and extreme competence in their field, mobilising the army in my opinion would be way too slow.
Edit: If I'm talking bollocks, let me know.
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