"Hurricane Katrina raised questions concerning the President's legal authority to send active duty military forces into a disaster area and the permissible functions the military can perform to protect life and property and maintain order. The Stafford Act authorizes the use of the military for disaster relief operations at the request of the state governor, but does not authorize the use of the military to perform law enforcement functions, which is ordinarily prohibited by the Posse Comitatus Act. However, the President may invoke other authorities to use federal troops to aid in the execution of the law, including the Insurrection Act, as amended and renamed by P.L. 109-364 (H.R. 5122/S. 2766). This report summarizes the possible constitutional and statutory authorities and constraints relevant to the use of armed forces, including National Guard units in federal service, to provide assistance to states when a natural disaster impedes the operation of state and local police."
CRS Report for Congress, RS22266