Want proof that NSA snooping thwarts terror plots? Stand by, senator says.

Americans will soon be able to judge for themselves the merits of National Security Agency programs to vacuum up massive amounts of digital data, because intelligence officials hope to declassify terrorist attacks thwarted by the controversial data-mining systems as early as Monday, the Senate’s top lawmaker on intelligence issues said Thursday.

Sen. Dianne Feinstein (D) of California, who chairs the Senate Intelligence Committee, told reporters that Director of National Intelligence James Clapper is working to declassify some examples of terrorist plots in the US and abroad that were thwarted by sweeping NSA phone-call and social-media data-collection systems. Mr. Clapper has previously said such surveillance efforts helped to block "dozens" of potential attacks.

Lawmakers who support the NSA’s intelligence gathering programs say they expect that the release of such information will significantly quell public outrage over them. New details about the programs came to light last week after they were leaked by self-described whistleblower and NSA contractor Edward Snowden.

“I hope at some point the order of magnitude of what they’ve done to keep America safe will become public,” said Sen. Bob Corker (R) of Tennesee after a closed-door briefing for senators with Clapper and other security officials. “It is my hope that that information, especially, will be declassified.”

Asked about Clapper’s claims that these programs foiled dozens of attacks, Senator Feinstein replied, “There’s more than you think.”

The scope and substance of NSA data-collection techniques have become a concern on Capitol Hill since Mr. Snowden, who held a top security clearance, leaked information on the programs to two newspapers.

Feinstein said one of the first legislative fixes will be to limit or prevent contractors from handling “highly classified technical data.”

She spoke after a classified briefing inside the Capitol. Besides Clapper, six national security officials, including representatives from the NSA, the FBI, and the Foreign Intelligence Surveillance Court, spoke with nearly half the Senate’s members, Feinstein said.

Feinstein and the intelligence panel’s top Republican, Sen. Saxby Chambliss of Georgia, have provided evidence that senators were offered briefings on the details of the NSA programs for several years. Even so, many senators expressed bewilderment and concern over the NSA’s ability to collect vast troves of data after the leaked NSA information hit the news media.  

Thursday's meeting was senators' second closed-door briefing with security officials since the program details were brought to light, and several senators said afterward that they now feel more comfortable with NSA actions.

“I wouldn’t say [my concerns] were 100 percent resolved, but I think some very good steps were taken today,” said Sen. Mike Johanns (R) of Nebraska, who had expressed concern about the NSA data-gathering earlier in the week. “I’m not sure I came out with a master's-degree understanding of it, but it was certainly a step in the right direction.”

Not everyone in the Senate felt the same way.

Sen. Rand Paul (R) of Kentucky, at a press conference earlier Thursday, decried the NSA’s "overreach" and vowed to sue the agency.

Leaving the intelligence briefing, Senator Paul had little to add: He pantomimed zipping and locking his lips as he shooed reporters away.