The Presidential Contender that Would Dismantle NSA Spying.

Bernie Sanders is running for president for many reasons, and you're going to hear about a lot of them on the campaign trail.

Income inequality. Campaign finance reform. Universal health care and climate change.

But quietly—at least relative to his wonk-laden sermons on economic populism—Sanders has for years also been one of the Senate's fiercest critics of the National Security Agency's secretive surveillance operations. And, unlike Hillary Clinton, he's been remarkably clear about where he stands.

The Vermont independent, who officially announced his White House bid on Thursday, is widely viewed by Beltway types as more of a debate-stage prop to bounce liberal ideas off Clinton on her march toward an inevitable Democratic primary victory. Polling has routinely placed Sanders in the single digits among Democratic voters. But while progressives are hopeful he can serve as an Elizabeth Warren surrogate and challenge Clinton on Wall Street reform, Sanders' candidacy also offers an opportunity to force Clinton to talk more concretely about domestic surveillance—something he has not minced words about since the Edward Snowden disclosures began in 2013.

"Kids will grow up knowing that every damn thing that they do is going to be recorded some place in a file, and I think that will have a very Orwellian and very inhibiting impact on the way we live our lives," Sanders told MSNBC's Chris Hayes just days after the initial batch of Snowden files emerged. "I want our law enforcement people to be vigorous in going after terrorists. But I happen to believe they can do that without disregarding the Constitution of the United States or the civil liberties of the American people."

Last year, Sanders sent a probing letter to Gen. Keith Alexander, then the head of the spy agency, demanding the answer to "one simple question": Has the NSA spied on members of Congress or other elected officials? (The answer, which came later: Probably.)

"I am deeply concerned about recent revelations that the National Security Agency (NSA) and other intelligence agencies are collecting enormous amounts of information about phone calls that Americans make, emails that we send, and websites that we visit," Sanders wrote then. "In my view, these actions are clearly unconstitutional."

But Sanders' skepticism of the intelligence agencies predates the Snowden revelations by more than a decade. While still serving in the House, he was one of just 66 members to vote against the post-9/11 Patriot Act, which greatly expanded the government's military and spying capabilities and eventually came to represent the legal justification for the NSA's bulk collection of U.S. call data. Sanders has also voted against reauthorizations of the Patriot Act, as well as the FISA Amendments Act in 2008.

And last year, Sanders voted for the Senate's USA Freedom Act, which would have effectively ended the phone-records program.

And though most of the media attention he receives revolves around his self-described democratic socialism, Sanders' hard-line defense of civil liberties is something many of his fans appreciate. One of his Senate Twitter account's most viral tweets quoted Sanders blasting the NSA:

What I worry about... #NSA #StopTheNSA pic.twitter.com/BKtCNsSl0K

— Bernie Sanders (@SenSanders) February 11, 2014

The Republican primary is filled with candidates (declared and otherwise) who have extremely divergent views on surveillance policy. While Sen. Marco Rubio and former Florida Gov. Jeb Bush applaud the NSA, Sen. Ted Cruz has worked with Democrats to reform it. Sen. Rand Paul has made ending the spy agency's domestic phone dragnet a central plank of his platform.

But Clinton has proven difficult to pin down, offering platitudes about "balancing civil liberties and security" when asked about surveillance but generally eliding specifics. With Sanders standing next to her on stage, Clinton may be pressured to get specific.