THE ESCALATING controversy over the National Security Agency's data mining program illustrates yet again how the Bush administration's intrusions on personal privacy based on a post-9/11 mantra of ''national security" directly threaten one of the enduring sources of that security: the Fourth Amendment ''right of the people to be secure in their persons, houses, papers, and effects, against unreasonable searches and seizures."
The Supreme Court held in 1967 that electronic eavesdropping is a ''search" within the meaning of the Fourth Amendment, recognizing that our system of free expression precludes treating each use of a telephone as an invitation to Big Brother to listen in. By 2001, the court had come to see how new technology could arm the government with information previously obtainable only through old-fashioned spying and could thereby convert mere observation -- for example, the heat patterns on a house's exterior walls -- to a ''search" requiring a warrant. To read the Constitution otherwise, the court reasoned, would leave us ''at the mercy of advancing technology" and erode the ''privacy against government that existed when the Fourth Amendment was adopted." This decision, emphasizing the privacy existing when the Bill of Rights was originally ratified in 1791, was no liberal holdover in conservative times. Its author was Justice Antonin Scalia. Justice Clarence Thomas joined the majority. Justice John Paul Stevens wrote the dissent. This issue should not divide liberals from conservatives, Democrats from Republicans.
These two decisions greatly undermine the aberrant 1979 ruling on which defenders of the NSA program rely, in which a bare Supreme Court majority said it doubted that people have any ''expectation of privacy in the numbers they dial," since they ''must 'convey' [such] numbers to the telephone company," which in turn can share them with others for purposes like ''detecting fraud and preventing violations of law." Unconvincing then, those words surely ring hollow today, now that information technology has made feasible the NSA program whose cover was blown last week. That program profiles virtually every American's phone conversations, giving government instant access to detailed knowledge of the numbers, and thus indirectly the identities, of whomever we phone; when and for how long; and what other calls the person phoned has made or received. As Justice Stewart recognized in 1979, a list of all numbers called ''easily could reveal . . . the most intimate details of a person's life."
The Fourth Amendment's guarantee against unconstrained snooping by Big Brother -- made bigger by an onrush of information-trolling technology that few foresaw in 1979 -- is bipartisan. It is a guarantee that cannot tolerate the pretense that numbers called from a private phone, unlike the conversations themselves, are without ''content." That pretense is impossible to maintain now that the technology deployed by NSA enables the agency to build a web with those numbers that can ensnare individuals -- all individuals -- just as comprehensively and intimately as all-out eavesdropping.
Even if one trusts the president's promise not to connect all the dots to the degree the technology permits, the act of collecting all those dots in a form that permits their complete connection at his whim is a ''search." And doing it to all Americans, not just those chatting with Al Qaeda, and with no publicly reviewable safeguards to prevent abuse, is an ''unreasonable search" if those Fourth Amendment words have any meaning at all.
The legal landscape, too, has changed decisively since the court's majority opined that Americans have no expectation of privacy in the numbers they call. Rejecting the accuracy of that description even decades ago, Congress, which was more vigorous then in its protection of privacy, enacted statutes reassuring us that our phone records would not be shared willy-nilly with government inquisitors without court orders. So it can no longer be said, if it ever could have been, that our ''expectations of privacy" about whom we call are groundless or that we ''consent" to reconstruction of our telephone profiles by using one of the phone companies that, unbeknownst to us, have agreed to share such information (although, we're told, not the content of every call) with NSA on demand.
Privacy apart, this president's defiance of statutes by the dozens is constitutionally alarming. But the matter goes deeper still. Even if Congress were to repeal the laws securing telephone privacy, or if phone companies found loopholes to slip through when pressured by government, the Constitution's Fourth Amendment shield for ''the right of the people to be secure" from ''unreasonable searches" is a shield for all seasons, one that a lawless president, a spineless Congress, and a complacent majority of citizens -- who are conditioned to a government operating under a shroud of secrecy while individuals live out their lives in fishbowls -- cannot be permitted to destroy, for the rest of us and our children.
Laurence H. Tribe is a professor of constitutional law at Harvard Law School and the Carl M. Loeb University Professor.