Jacob Sullum
After her purse was snatched in 1976, Patricia McDonough began receiving threatening phone calls from a man who identified himself as her robber. Following one of the calls, she saw a car she recognized from the scene of the crime slowly pass by her house in Baltimore.

Police later spotted the same car in McDonough's neighborhood, driven by a man who matched her description of the purse snatcher, and used the license plate number to identify the owner as Michael Lee Smith. Based on this information, the police asked the phone company to install a "pen register," which recorded the numbers dialed by Smith for a couple of days. One of those numbers was McDonough's.

As a federal judge pointed out on Monday, this brief monitoring of a specific criminal suspect bears little resemblance to the National Security Agency's comprehensive database of phone records, which includes information about every call placed in the United States during the past five years. Yet the Obama administration argues that Smith v. Maryland, the 1979 decision in which the Supreme Court approved the warrantless surveillance that incriminated Smith, means there is no constitutional problem with treating every American as a potential terrorist. Amazingly, the government's interpretation may be right.

U.S. District Judge Richard Leon, who issued a preliminary injunction against the NSA's database, rejected the government's reliance on Smith. Not only is the NSA casting a vastly wider net than the cops in Baltimore, he said, but the ubiquity of cellphones makes telephone "metadata" -- information about who called whom, when and for how long -- much more revealing than it used to be.

"Records that once would have revealed a few scattered tiles of information about a person now reveal an entire mosaic -- a vibrant and constantly updating picture of the person's life," Leon wrote. "The Smith pen register and the ongoing NSA Bulk Telephony Metadata Program have so many significant distinctions between them that I cannot possibly navigate these uncharted Fourth Amendment waters using as my North Star a case that predates the rise of cellphones."

Leon's argument would be compelling if Smith did not include sweeping language that seems to rule out Fourth Amendment challenges to government collection of information about you, no matter how sensitive, if you have divulged it to someone else. "This Court consistently has held," the justices said, "that a person has no legitimate expectation of privacy in information he voluntarily turns over to third parties."

Jacob Sullum

Jacob Sullum is a senior editor at Reason magazine and a contributing columnist on Townhall.com.
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