Legal Authorities Supporting the Activities of the National Security Agency Described by the President, US Department of Justice, January 19, 2006 [white paper saying that the NSA activities are supported by the president's position as Commander in Chief and congressional authorization for the war on al Qaeda under the 2001 Authorization to Use Military Force, and moreover "fall within a well-established exception to the warrant requirement and [satisfy] the Fourth Amendment's fundamental requirement of reasonableness"]. Read the full text of the white paper [PDF]. Reported in JURIST's Paper Chase here.