There is a crucial difference between the Obama administration’s phone call data-mining program, which is constitutional under current law, and the Bush administration’s NSA surveillance program, which was clearly unconstitutional. Unlike the Obama program, which is limited to obtaining information about phone calls made and received from telephone companies, the Bush program authorized the government to wiretap private phone conversations. From a constitutional perspective, the difference is critical, and it is unfortunate that President Obama has not done a better job of explaining the distinction, and why his administration’s program does not violate the constitutional “right of privacy.”

The Fourth Amendment provides that “the right of the people to be secure in their persons, houses, papers, and effects, against unreasonable searches and seizures, shall not be violated.” The Supreme Court has held that, at least presumptively, a search is “unreasonable” unless it is based on probable cause and a judicial warrant.
It would therefore seem that it violates the Fourth Amendment for the government to collect phone call records from phone companies without first obtaining a judicial warrant based on a finding that there is probable cause to believe that the individual whose call records the government want to examine has committed a crime. This would be true, for example, if the government wanted to open that individual’s mail or search his home or wiretap his phone calls, so why isn’t it true in this situation as well?
The puzzle turns on the meaning of the word “search.” The Fourth Amendment does not protect a general right of privacy, but only a right not to have the government unreasonably search an individual’s person, house, papers, or effects. But what is a “search”?
The Supreme Court first confronted the meaning of “search” in its 1928 decision in Olmstead v. United States. In that case, the Court held that a wiretap of a phone call was not a “search” within the meaning of the Fourth Amendment because it did not involve a physical intrusion into a constitutionally protected place. The Court explained that what the Framers meant by a “search” was a physical intrusion into an individual’s pocket, briefcase, home, or envelope. A wiretap, which is effected without entering the suspect’s home, is therefore not a “search” for purposes of the Fourth Amendment. Thus, the government could constitutionally wiretap phone calls without either probable cause or a warrant as long as it did not physically enter the target’s home or business.
This remained the law until 1967, when the Supreme Court, in Katz v. United States, overruled Olmstead and held that the use of a bugging device by the police on the outside of a public telephone booth to overhear a phone call within the booth was nonetheless a “search” within the meaning of the Fourth Amendment.
The Court explained that the Fourth Amendment “protects people, not places,” and that a physical intrusion into a constitutionally protected place was not necessary for the Fourth Amendment to come into play. The central question, the Court held, was whether the government’s action invaded an individual’s “reasonable expectations of privacy.”
In the modern world, the Court held, a bugging device on the outside of a telephone booth or a wiretap on a telephone constitutes a “search,” even though they involve no physical intrusion into a constitutionally protected place, because they violate our “reasonable expectations of privacy.”
But Katz immediately gave rise to the question: What is a “reasonable expectation of privacy”? Suppose X has a conversation at a dinner party at which he reveals certain information about himself to the other guests. Thereafter, the government subpoenas one of the guests and compels her to testify about what X told her at the party. Is this a “search” within the meaning of the Fourth Amendment?
In a series of decisions in the years after Katz, the Supreme Court said “no.” As the Court observed in Katz, “what a person knowingly exposes to the public is not a subject of Fourth Amendment protection.” Thus, as a general matter, one has no “reasonable expectation of privacy” when one reveals information to third parties. Because those individuals are free to tell others what they were told, the speaker has no “reasonable expectation” that such conversations are “private.”
In United States v. Miller, decided in 1976, the Supreme Court considered the following question: Is it a “search” within the meaning of the Fourth Amendment for the government to subpoena information from a bank about a depositor’s financial transactions? Surely, one’s financial transactions are “private,” right? The Court said “no.”
Because the depositor had “voluntarily conveyed” his financial information to the bank and its employees,” who were complete strangers to the depositor, the depositor assumed the risk “that the information would be conveyed by the bank to the government.” Hence, the Court held, the depositor had no “reasonable expectation of privacy” in the information and there was therefore no “search” of the depositor when the government obtained the information from the bank.
Three years later, in Smith v. Maryland, the Court extended this logic to a pen register, a device that collects all the numbers called from a particular phone. Without probable cause or a warrant, the police, who suspected Smith of a crime, installed a pen register on Smith’s calls at his telephone company. The Supreme Court held that this was not a “search” for purposes of the Fourth Amendment, because people know that the phone company keeps records of their phone calls, “a person has no legitimate expectation of privacy in information he voluntarily turns over the third parties,” and Smith voluntarily “assumed the risk that the company would reveal to police the numbers he dialed.”
It is on the basis of this line of decisions that commentators have correctly stated that, under existing law, the government’s program of collecting phone-call data from phone companies does not violate the Fourth Amendment.
This is not to say, of course, that the Supreme Court decisions are “correct.” In his dissenting opinion in Miller, for example, Justice William J. Brennan, Jr. objected that an individual should be held to retain a “reasonable expectation of privacy” in the financial records he discloses to his bank, because such disclosures are “not entirely volitional in circumstances in which “it is impossible to participate in the economic life of contemporary society without maintaining a bank account” and because, in the course of his financial transactions with his bank, a depositor inevitably “reveals many aspects of his personal affairs, opinions, habits and associations.”
But even if Miller and Smith are correct in terms of the meaning of the Fourth Amendment, the mere fact that government can constitutionally exercise its authority in this manner does not mean that it should do so. That something is constitutionally permissible does not make it sound public policy.