Ronald Reagan issued Executive Order 12333 in 1981, reversing the Carter and Ford reforms of government surveillance (sparked by the Church Commission, convened in the wake of Nixon's wiretapping scandal); GWB expanded it twice more, once during each term.
This order is the legal cover and excuse deployed internally by spy agencies when they break the law and violate the Constitution. In Ars Technica, Cyrus Farivar tracks down many internal memors, and statements from a wide variety of ex-spies, including the famous NSA whistleblowers Bill Binney and Thomas Drake, to paint a vivid picture of how 12333 is the all-purpose excuse for any kind of funny business. Farivar also notes that Snowden asked several pointed questions about 12333, without getting any kind of satisfactory answers, before he left the NSA, taking many damning documents with him.
Thirty-year NSA veteran William Binney told Ars that drastic measures such as the NSA’s Fairview program—described by other intelligence whistleblowers as the NSA’s project to “own the Internet”—are also authorized under EO 12333.
“This program was started at least back in 2001 and has expanded to between 80 and 100 tap points on the fiber optic lines in the lower 48 states,” he said by e-mail. “Most of these fiber optic tap points are not on the East or West coast. This means that the primary target of this collection is domestic... Most collection of US domestic communications and data is done under EO 12333, section 2.3 paragraph C in the Upstream program. They claim, near as I can tell, that all domestic collection is incidental. That’s, of course, the vast majority of data.”
Specifically, that subsection allows the intelligence community to "collect, retain, or disseminate information concerning United States persons" if that information is "obtained in the course of a lawful foreign intelligence, counterintelligence, international narcotics or international terrorism investigation."'
The executive order that led to mass spying, as told by NSA alumni [Cyrus Farivar/Ars Technica]