Memorandum for the Attorney General: Re: Review of the Legality of the [President's Surveillance] Program [May 6, 2004] [open pdf - 2MB]
"You have asked this Office to undertake a thorough reexamination of the [President's Surveillance] program as it is currently operated to confirm that the actions that the President has directed the Department of Defense to undertake through the National Security Agency (NSA) are lawful. [The President's Surveillance Program] is a highly classified and strictly compartmented program of electronic surveillance within the United States that President Bush directed the Department of Defense to undertake on October 4, 2001 in response to the attacks of September 11, 2001. Specifically, the program is designed to counter the threat of further terrorist attacks on the territorial United States by detecting communications that will disclose terrorist operatives, terrorist plans, or other information that can enable the disruption of such attacks, particularly the identification of al Qaeda operatives within the United States. The President's initial directive to the Secretary of Defense authorized the [President's Surveillance] program for 30 days. Since then, the President has periodically (roughly every 30 to 45 days) reauthorized the program."
U.S. Dept. of Justice: http://www.justice.gov/