Many Americans reacted with outrage when they learned that the NSA stores details about phone calls made by virtually everyone in the United States. They felt a strong, if vague, notion that the practice must violate their constitutional rights. Couldn't NSA analysis of telephone metadata reveal sensitive, private details about most anyone in the country, like their network of friends, the identity of their sexual partners, or their contact with medical or mental health professionals? Aren't mass searches of innocents anathema to the Fourth Amendment?
The legal response from NSA defenders has leaned heavily on the precedent set in Smith v. Maryland, a Supreme Court case decided in 1979, before the era of big data.
The case concerned a robbery. Patricia McDonough, the victim, noticed a 1975 Monte Carlo near the scene of the crime. Later she received obscene phone calls from a man who claimed to be the robber. Once he asked the victim to step out onto her porch, where she saw the Monte Carlo drive slowly by. Soon after, police spotted a man driving the Monte Carlo in the victim's neighborhood. After tracing its license plate to Michael Lee Smith, officers went to the phone company and asked them to put a pen register on his phone. The resulting phone records showed that he called the victim's house. At trial, he tried to suppress that evidence, arguing that the police should have gotten a warrant before having the phone company track the numbers he dialed.
He lost at the Supreme Court. In the majority opinion, Justice Harry Blackmun invoked a test articulated in a previous case, Katz v. United States. It declared that, for Fourth Amendment purposes, a search only occurs when a citizen has a reasonable expectation of privacy.
Did the robber who used his home phone to call his victim have that? "We doubt that people in general entertain any actual expectation of privacy in the numbers they dial," Blackmun wrote. "All telephone users realize that they must 'convey' phone numbers to the telephone company, since it is through telephone company switching equipment that their calls are completed. All subscribers realize, moreover, that the phone company has facilities for making permanent records of the numbers they dial, for they see a list of their long-distance calls on their monthly bills."
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The Fourth Amendment confers not "a right to privacy," but a right to be secure against "unreasonable searches and seizures." The NSA's defenders argue that, under the precedent set in Smith v. Maryland, the NSA is not conducting unreasonable searches, because the tens of millions of Americans whose telephone data it hoovers up and stores have no expectation of privacy in who they call. By this logic, even if the federal government used powerful computers to look through the phone calls of tens of millions of people and fully mapped the associations of every last American, based on all phone calls made over the last five years, their conduct still wouldn't count as a search for the purposes of the Fourth Amendment, even if they also published a list of everyone who dialed up a therapist, a divorce attorney, a suicide hotline, an Islamic charity, or the ACLU or NRA!
In contrast, if the government eavesdropped on the content of even a single telephone call without a warrant, that would be a violation of the Fourth Amendment, even though virtually every American would place a much higher value on the private details revealed by the sum total of the metadata that they generate.
At the time Smith v. Maryland was decided, the courts did not anticipate this seemingly absurd result, in part because the case was decided prior to the era of cheap data storage, modern computing power, and sophisticated network analysis. "It is not possible to argue honestly that the facts of Smith are anything like the NSA’s bulk data collection," Jim Harper argued at the Cato Institute's blog. "The police had weighty evidence implicating one man. The telephone company voluntarily applied a pen register, collecting analog information about the use of one phone line by that one suspect. I can’t think of a factual situation that could be at a further extreme than NSA’s telephone calling surveillance program." *
Judge Richard Leon made a similar argument when he found that the NSA's bulk collection of telephone metadata is, in fact, a violation of the Constitution.
But since a different federal judge has just invoked Smith while reaching a contrary conclusion—that the Fourth Amendment does not prohibit bulk metadata collection—it's worth dwelling on what embracing the NSA's reading of Smith would really mean, and why doing so is an unsound approach to interpreting the Constitution, even if we forget about the present controversy and speak more generally.
To illustrate what I mean, indulge a hypothetical I dreamt up while trying to articulate to myself why I find the way Smith is being invoked so illegitimate and dangerous.
Like most Americans, I go with some regularity to the barber shop. I sit down in the chair, the barber goes to work with his scissors, and by the end of the cut my hair is strewn about the floor. As I pay at the register, the barber sweeps up my hair and dumps it into a trashcan. It subsequently goes out to the dumpster in back. By the logic of Smith, I have no reasonable expectation of privacy as regards this hair. I freely allow it to be clipped from my head and to fall to the floor, knowing full well that third parties will take possession of it en route to the dump.
For the sake of this hypothetical, let us imagine two technological advances that take place 10 years apart. In 2015, a shampoo is introduced that prevents any hair washed with it from revealing the DNA of the person to whom it belongs. Widely used in barber shops, it renders the fact that I have no reasonable expectation of privacy in the hair I leave on the barbershop floor completely unproblematic. There is no scenario in which authorities could perpetrate serious, widespread abuses using hair taken from the floors of barbershops. And anyone could easily protect the privacy of the DNA in their hair, as a 2016 Supreme Court opinion notes while upholding the police's ability to gather hair from dumpsters.