“Ten days after the attacks [September 21, 2001], [Deputy Chief in the Office of Legal Counsel John] Yoo wrote an internal memo arguing that the NSA [National Security Agency] could use ‘electronic surveillance techniques and equipment that are more powerful and sophisticated than those available to law enforcement agencies in order to intercept telephonic communications and observe the movement of persons but without obtaining warrants for such uses.’ He noted that while such unprecedented and intrusive actions might be rejected on constitutional grounds during normal times, they are now justified as a result of the 9/11 attacks. During such times, he said, ‘the government may be justified in taking measures which in less troubled conditions could be seen as infringements of individual liberties.’ “
– James Bamford, The Shadow Factory, Pages 115-116