The Pentagon has assumed that the Posse Comitatus Act(18 U.S.C. 1385), the Civil War era law which prevents the use of federal troops as law enforcement on US soil, has already been overturned.

Using the pretense of enforcing quarantine in case of an avian flu pandemic or another natural disaster, the US Defense Department has continued in its legally questionable planning for using US troops in future "natural disasters" or "terrorist incidents."

In an article called "Pentagon Plans to Beef Up Domestic Rapid- Response Forces," the Washington Post writes that "Paul McHale, Assistant Secretary of Defense for Homeland Defense, stressed, however, that the expanded active-duty military response would be limited to rare, mass calamities or attacks in which thousands of lives were at risk -- such as a category 4 hurricane, or a terrorist strike involving chemical, biological or nuclear weapons."
http://www.washingtonpost.com/wp-dyn/content/article/2005/10/12/
AR2005101202018_pf.