From John Dean:

Presidential Powers Regarding National Security: A Nixonian View

Nixon famously claimed, after resigning from office, that when the president undertook an action in the name of national security, even if he broke the law, it was not illegal.

Nixon's thinking (and he was learned in the law) relied on the precedent established by Abraham Lincoln during the Civil War. Nixon, quoting Lincoln, said in an interview, "Actions which otherwise would be unconstitutional, could become lawful if undertaken for the purpose of preserving the Constitution and the Nation."

David Frost, the interviewer, immediately countered by pointing out that the anti-war demonstrators upon whom Nixon focused illegal surveillance, were hardly the equivalent of the rebel South. Nixon responded, "This nation was torn apart in an ideological way by the war in Vietnam, as much as the Civil War tore apart the nation when Lincoln was president." It was a weak rejoinder, but the best he had.

Nixon took the same stance when he responded to interrogatories proffered by the Senate Select Committee on Government Operations To Study Intelligence Operations (best know as the "Church Committee," after its chairman Senator Frank Church).

In particular, he told the committee,

"In 1969, during my Administration, warrantless wiretapping, even by the government, was unlawful, but if undertaken because of a presidential determination that it was in the interest of national security was lawful. Support for the legality of such action is found, for example, in the concurring opinion of Justice White in Katz v. United States."

(Katz is the opinion that established that a wiretap constitutes a "search and seizure" under the Fourth Amendment, just as surely as a search of one's living room does - and thus that the Fourth Amendment's warrant requirements apply to wiretapping.)

Nixon rather presciently anticipated - and provided a rationalization for - Bush:

He wrote, "there have been -- and will be in the future -- circumstances in which presidents may lawfully authorize actions in the interest of security of this country, which if undertaken by other persons, even by the president under different circumstances, would be illegal."

Even if we accept Nixon's logic for purposes of argument, were the circumstances that faced Bush the kind of "circumstances" that justify warrantless wiretapping? I believe the answer is no.