President Bush's post- Sept. 11, 2001, authorization to the National Security Agency to carry out electronic surveillance into private phone calls and e-mails is consistent with court decisions and with the positions of the Justice Department under prior presidents.
The president authorized the NSA program in response to the 9/11 terrorist attacks on America. An identifiable group, Al Qaeda, was responsible and believed to be planning future attacks in the United States. Electronic surveillance of communications to or from those who might plausibly be members of or in contact with Al Qaeda was probably the only means of obtaining information about what its members were planning next. No one except the president and the few officials with access to the NSA program can know how valuable such surveillance has been in protecting the nation.
In the Supreme Court's 1972 Keith decision holding that the president does not have inherent authority to order wiretapping without warrants to combat domestic threats, the court said explicitly that it was not questioning the president's authority to take such action in response to threats from abroad. Four federal courts of appeal subsequently faced the issue squarely and held that the president has inherent authority to authorize wiretapping for foreign intelligence purposes without judicial warrant.
In the most recent judicial statement on the issue, the Foreign Intelligence Surveillance Court of Review, composed of three federal appellate court judges, said in 2002 that "All the ... courts to have decided the issue held that the president did have inherent authority to conduct warrantless searches to obtain foreign intelligence ... We take for granted that the president does have that authority."
The passage of the Foreign Intelligence Surveillance Act in 1978 did not
alter the constitutional situation. That law created the Foreign Intelligence Surveillance Court that can authorize surveillance directed at an "agent of a foreign power," which includes a foreign terrorist group. Thus, Congress put its weight behind the constitutionality of such surveillance in compliance with the law's procedures.
But as the 2002 Court of Review noted, if the president has inherent authority to conduct warrantless searches, "FISA could not encroach on the president's constitutional power."
Yes, yes, I know...mere partisan spin.
Please note however that the above declaration regarding Bush's Constitutional authority is not my own. The statement was made by John Schmidt who served under President Clinton from 1994 to 1997 as the associate attorney general of the United States.
More of his take, here