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“In the 215 program you’ve got all three branches going check, check, check. That’s kind of the Madisonian trifecta. That’s how it’s supposed to work,” he said.

He said there have been no abuses of the bulk data collection program — and was challenged by the ACLU’s Ms. Murphy, who interjected, “That we know of.”

Mr. Hayden then pointed to Mr. Medine, who, as chairman of the oversight board, had classified access. “He’s looked at the program [and] he says there’s no abuse.”

Mr. Medine didn’t dispute that, but he said there’s reason to be “cautious” the more data the government is given and how it’s used. He cited the Census Bureau’s collection of information that the government used during World War II to round up Japanese Americans for internment.

Mr. Medine also questioned the need for the metadata bulk collection in the first place. His board’s report contradicted the intelligence community’s initial assertions that it had prevented some potential terrorist attacks through the bulk collection program.

“The phone metadata program [isn’t needed] because there are alternative ways of getting access to the program that serve the same, and maybe even better, ends,” he said.

Mr. Hayden said that’s true — for now.

“It’s better because we can afford more time. It may not have been the right answer in 2002. But now [it may be right] given what we know of al Qaeda, the degree of threat, all the other intelligence tools we have — and that’s an important point,” Mr. Hayden said.

For his part, Mr. Lee questioned the current status of court decision-making on bulk data, saying he doubted whether prior Supreme Court precedent anticipated, or is appropriate for, a 21st century level of technological exchange — and the government’s ability to monitor it.

“What might have been stored on papers and personal effects inside our physical houses in the 1790s would not necessarily be put onto a piece of tangible paper today,” said Mr. Lee, a Utah Republican. “Nonetheless, these same privacy concerns still need to be protected, and I think some of the programs we’re talking about today threaten to undermine those same privacy and security interests that are at the heart of the Fourth Amendment.”

He said the question is more complex than just a straight question of constitutionality because no final court has yet ruled the programs unconstitutional — and given various rules, it’s “difficult to conceive of the precise procedural route” that a case would take to reach the Supreme Court.