In debates about the NSA’s mass surveillance of all our phone calling, pro-government lawyers have often tried to play a trump card called Smith v. Maryland. Smith is a 1978 Supreme Court decision as right for our times as laws requiring public buildings to provide spittoons. But lawyering rightly relies heavily on precedent, so there it was, the argument that people don’t have a constitutional interest in data about their phone calling because a suspected burglar and obscene phone-caller didn’t have such an interest back in 1976.

D.C. district court judge Richard Leon ruled today that Smith is not an appropriate precedent for considering the constitutionality of the NSA’s mass surveillance program. “[T]he Smith pen register and the ongoing NSA Bulk Telephony Metadata Program,” he concluded, “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 cell phones.”

When phone calling was home- or office-bound and relatively rare, people’s interest in the information about their calling was not as great as it is today. Cell phones now accompany most people everywhere they go every single day. “[T]he ubiquity of phones has dramatically altered the quantity of information that is now available and, more importantly, what that information can tell the Government about people’s lives.” (emphases omitted)

Judge Leon applied the “reasonable expectation of privacy” test in finding that he is likely to determine that the NSA’s data seizures are a Fourth Amendment violation, even though that standard has been thrown into doubt by recent Supreme Court decisions. But what is important is that his decision breaks the circular logic adopted by the panels of judges ratifying mass domestic surveillance under the Foreign Intelligence Surveillance Act. These panels believed they could act in secret because of the premise that Americans don’t have a constitutional interest in data about their calls. Their secret operations barred Americans from contesting that premise. And the band played on. Until someone leaked this mass domestic spying to the public.

Judge Leon’s assessment of the government’s interest is notable. He picked up on the fact that the government’s collection of data about all our calls is simply to make things a little quicker when they want to do an investigation.

“[T]he Government’s interest,” he writes, “is not merely to investigate potential terrorists, but rather, to do so faster than other methods might allow. … Yet … the Government does not cite a single instance in which analysis of the NSA’s bulk metadata collection actually stopped an imminent attack, or otherwise aided the Government in achieving any objective that was time-sensitive in nature.” (emphases omitted)

Databasing of all our calls is a convenience and not a necessity. That stacks up poorly against the privacy costs all Americans suffer by having their phone-calling catalogued in government databases.

There will almost certainly be an appeal, and there will be more cases coming up through the courts that explore the many dimensions of this issue. But now we can tell our lawyer friends who have been a little too slavish to precedent that Smith v. Maryland is not good law.