On Tuesday, Cruz echoed Wyden’s attack. “I would note that Marco knows what he’s saying isn’t true,” Cruz said. He leaned on statistics to make his point, claiming that the previous program covered 20 to 30 percent of phone numbers, while the new program covers “nearly 100 percent.”

Rubio eyed him in discomfort. “I don’t think national television in front of 15 million people is the place to discuss classified information,” he said. He went on to repeat his claim that the NSA reform bill gave the agency no new powers.

Almost immediately, the communications director for Richard Burr, the chairman of the Senate Intelligence Committee, tweeted, “Cruz shouldn’t have said that.” And this morning, Burr said he had requested that his staff look at transcripts of the debate in order to determine whether Cruz had leaked classified information.

Burr later clarified that his committee would not be formally investigating Cruz’s remarks. But his earlier comment was a reminder to presidential candidates and voters that one of the government’s most powerful and controversial national-security tools is not up for public debate.

On the issue of NSA surveillance, Burr’s position is closer to Rubio’s than Cruz’s. He and Rubio voted together this summer to oppose the end of the NSA’s bulk metadata program, and after the bill to curtail the program passed, he said the agency is unlikely to use the new system at all because it’s too cumbersome to be effective.

The backlash to Cruz’s remarks reinforces the lack of an open, democratic discussion of surveillance programs. And although elements of the programs must remain classified to preserve their effectiveness, the total blackout on information about them keeps the public from being able to make informed decisions about the lawmakers and officials they elect.

“Sure, we can talk about the capabilities of Section 702,” said Jake Laperruque, a fellow at New America’s Open Technology Foundation, referring to a different NSA program that scoops up data straight from the physical infrastructure of the Internet. “But it’s hard to have a meaningful debate about it when you can’t tell the American people whether a few hundred or a few million of them are being swept up in a warrantless surveillance program.”

The classified nature of the NSA’s surveillance programs has also gotten in the way of attempts to rein in the agency’s power in a court of law. Time and time again, judges have thrown out lawsuits brought against the NSA by civil-liberties advocacy organizations like the ACLU, on the grounds that it’s nearly impossible to prove that a particular plaintiff was affected by its spying. Other cases have died when judges have decided that plaintiffs could not win without classified information being disclosed.

Meanwhile, the NSA has been operating its new phone-metadata surveillance program for nearly three weeks. The vast array of presidential candidates from both parties have taken up positions on surveillance, ranging from the firmly pro-privacy Rand Paul and Bernie Sanders, to the staunchly pro-NSA Rubio. But with voters unable to understand the extent to which the agency’s programs suck up their own personal information along with the information of potential terrorists, they are poorly situated to choose among those positions.