Just 10 days later, another federal judge, sitting in New York, issued another decision in a separate lawsuit involving NSA surveillance, and found no constitutional problems. Not only is the program constitutional, but the government actually provided evidence that its use had headed off planned attacks by al-Qaeda, said Judge William H. Pauley III.
"No doubt, the bulk metadata-collection program vacuums up information about virtually every telephone call to, from, or within the United States," Pauley wrote. "This is by design, as it allows the NSA to detect relationships so attenuated and ephemeral they would otherwise escape notice. As the Sept. 11 attacks demonstrate, the cost of missing such a thread can be horrific."
How could two judges, ruling on the same issue and with essentially the same set of facts, come to conclusions so wildly at odds?
In fact, it happens in federal courts all the time. And if clashing decisions are upheld by respective appeals panels, then it is very often up to the Supreme Court to sort out the differences.
Such contrasting results are even more likely when a legal dispute involves fast-paced technological changes.
"It is not surprising for lower courts to come to completely opposite conclusions on constitutional questions, because constitutional arguments are so malleable," said Jeffrey Rosen, president and CEO of the National Constitution Center and a professor of law at George Washington University Law School.
The lawsuit before Leon was brought by Charles Strange, who said that his Verizon phone records had been accessed by the NSA and that he was a likely target of surveillance. Strange's son Michael, a Navy cryptologist, was killed with a SEAL team in 2011 when their helicopter was shot down in Afghanistan.
The elder Strange filed suit after former NSA contract worker Edward Snowden leaked information to the New York Times and the British newspaper the Guardian detailing the agency's extensive data-collection programs.
Quite apart from Snowden's revelations, both federal and state courts increasingly have been grappling with the question of how to oversee anticrime and terrorism programs.
In 2012, the U.S. Supreme Court ruled unanimously that police must first obtain a warrant before placing a GPS tracking device on the car of a crime suspect. The decision came in the case of a suspected drug dealer who the government said had no expectation of privacy since he was traveling on public roads. But the court said the police tactic was tantamount to trespass and violated the Fourth Amendment's protection against unreasonable searches and seizures.
In July, in another precedent-setting decision, the New Jersey Supreme Court found that local police had breached constitutional protections by tracking the cellphone calls of a burglary suspect without a warrant. Cellphone data can pinpoint the whereabouts of a person to within a few yards, and such searches, conducted without a warrant, violate a person's right to privacy, the court said.
For decades, government access to telephone company records was governed by the 1979 U.S. Supreme Court decision in Smith v. Maryland. The court said citizens had no expectation of privacy regarding phone records since they voluntarily turn over their records to the phone company. But Leon found that the circumstances had changed so much since 1979 that the court's earlier reasoning might not apply.
"In an age when all of our data is stored" on computers and mobile phones, Rosen said, "I think that Judge Leon persuasively argued that the world has changed since the 1979 case."
But Pauley has passionate defenders who insist that the nature of the information the government is seeking hasn't changed, despite changes in technology. The NSA is merely sweeping up phone numbers, they say. It effectively knows nothing about the people who possess those numbers. If a U.S. citizen is in telephone contact with a suspected terrorist, then the information is turned over to the FBI for investigation.
Claire Finkelstein, a professor at the University of Pennsylvania Law School and director of its Center for Ethics and the Rule of Law, said Pauley was correct, at least in his interpretation of where the constitutional boundaries lie - that bulk collection of telephone data was constitutional.
Finkelstein said she was less concerned about the NSA surveillance program than over the court that has responsibility for keeping the agency in line, the Foreign Intelligence Surveillance Act court, because it operates in secret. While such courts must operate in secrecy, because they deal in sensitive national-security information, said Finkelstein, the potential for abuse is considerable.