But it may be that nothing turns on that. Writing recently in Judicature magazine, Judge Douglas H. Ginsburg, who was appointed to the District of Columbia Circuit by President Ronald Reagan, noted with satisfaction that a recent empirical study had absolved his court “of the charge, so often leveled in the vacuous but vociferous political debates over the confirmation of a new judge, that the court is a political partisan.”

His own 2010 opinion in United States v. Maynard, writing for a unanimous three-judge panel with two judges appointed by a Republican president, tends to illustrate his point. The decision, which will be helpful to the challengers to the data collection program, was, curiously, mentioned only in passing by Judge Leon.

Judge Ginsburg said the collection of huge troves of data over long stretches of time, producing a mosaic of information, could cross a constitutional line.

“A person who knows all of another’s travels,” Judge Ginsburg wrote, “can deduce whether he is a weekly churchgoer, a heavy drinker, a regular at the gym, an unfaithful husband, an outpatient receiving medical treatment, an associate of particular individuals or political groups — and not just one fact about a person, but all such facts.”

Alexander A. Abdo, an A.C.L.U. lawyer, echoed that reasoning at the Nov. 22 argument in the New York case, four days after arguments in the case heard by Judge Leon. The telephone records collected by the security agency reveal, Mr. Abdo said, “who you call and when, whether you call your doctor, the domestic violence hotline, an abortion provider, an ex-girlfriend, a suicide hotline or a pastor,” he said. “And it reveals not just one of those details about every American, but every one of those details.”

The District of Columbia Circuit’s decision, Mr. Abdo said, “could serve as a model for this court.”

In 1979, in Smith v. Maryland, the Supreme Court said a robbery suspect could not expect that his right to privacy extended to the numbers dialed from his phone. The government says the Fourth Amendment analysis in the new cases should begin and end with that decision.