Supporters of Sen. Mark Udall, D-Colo., say his possible re-election loss to Republican Rep. Cory Gardner would be a significant setback for privacy and mass surveillance reform.

The Hill reported Sunday that Udall’s potential defeat has some civil liberties activists worried, and the libertarian publication Reason warned Monday his loss would “further dim the prospects of real reform to America's burgeoning surveillance state.”

Gardner says that’s not true.

The two-term congressman voted in July 2013 for the narrowly defeated Amash amendment, which sought to end the National Security Agency’s mass collection of U.S. phone records, and in June voted for the Lofgren-Massie amendment, which would end “backdoor” NSA data collection on Americans.

In May, Gardner joined many other privacy-minded congressmen in voting against the NSA-reforming USA Freedom Act after initially co-sponsoring it. The bill would end the automatic collection of all U.S. phone records, but was weakened at the behest of the Obama administration and NSA allies.

“I felt House leadership had stripped it down and watered it down and Sen. Udall actually sent out a tweet agreeing with my vote,” he says.

Gardner is co-sponsoring legislation to require law enforcement to get warrants for emails stored longer than 180 days and hopes to vote for greater oversight of the Foreign Intelligence Surveillance Court.

Udall and Sen. Ron Wyden, D-Ore., members of the Senate Intelligence Committee, issued vague warnings about NSA mass surveillance before whistleblower Edward Snowden leaked documents exposing the agency's phone and Internet spy programs.

Though Udall was then and is now a critic of mass surveillance, the reporters who worked most closely with Snowden – Glenn Greenwald and Laura Poitras – sharply criticized his decision not to invoke the Constitution’s speech or debate clause in order to disclose classified information on the NSA programs.

“Mark Udall and Ron Wyden lacked the courage to do what they should have done, which is gone to the floor of the Senate, invoke the immunity that the Constitution gives them and reveal this information,” Greenwald told a Georgetown University audience in April.

Gardner says he is open to using the constitutional privilege if he learns of programs he considers egregious violations of Americans’ constitutional rights.

“Every member of the Senate has a constitutional duty to follow the Constitution and to uphold the Constitution,” he says.

“I don’t want to speculate on examples,” he clarifies. “But, again, I believe every member of the Senate, every member of the House, has an obligation to uphold the Constitution.”

Gardner voted in 2011 to extend provisions of the Patriot Act and in 2012 to extend Foreign Intelligence Surveillance Act amendments that officials secretly reinterpreted as allowing bulk phone and Internet surveillance. Udall voted against the measures.

Gardner says he researched surveillance issues and became alarmed by apparent violations of Americans’ rights after those votes, following Snowden's leaks to the media.

“There’s a lot of people who have concerns that their rights are being violated in terms of data collection, in terms of email privacy [protections] that they had assumed were always in place,” he says. "We have to protect the rights of the American people."

Gardner declined to say if he believes Snowden’s decision to risk prison by leaking classified documents was patriotic.

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Though well-regarded by privacy advocates, Udall said in December that Snowden “broke his oath, he broke the law” and should “come home [and] make the case that somehow there was a higher purpose here.” Skeptics of that suggestion say most court proceedings would be closed to the public and that overclassification would make any trial unfair.