Terrorism: Some Legal Restrictions on Military Assistance to Domestic Authorities Following a Terrorist Attack [Updated May 27, 2005] [open pdf - 35KB]
"The Constitution empowers the President to act as Commander in Chief of the armed forces and to see to the execution of federal law; it gives Congress the authority to make federal law including laws for the regulation of the armed forces. The Posse Comitatus Act prohibits use of the armed forces to perform civilian governmental tasks unless explicitly authorized to do so. There are statutory exceptions to ensure continued enforcement of state and federal law, to provide disaster assistance, and to provide technical support for law enforcement. Further exceptions are proposed (H.R. 1986, H.R. 1815). There are constitutional impediments to the use of the military to nationalize an industry, to try civilians, and to compel state officials to perform federally-imposed duties. Unlawful use of the armed forces might result in criminal or civil liability for responsible authorities and frustrate prosecution of terrorists. For a more complete discussion, see CRS Report 95-964, 'The Posse Comitatus Act and Related Matters: The Use of the Military to Execute Civilian Law."
CRS Report for Congress, RS21012