The National Security Agency, accustomed to operating in the shadows, has had a rough few months as details of its secret intelligence-gathering operations have been leaked. The Washington Post reported today that the agency has violated its privacy rules and exceeded its authority thousands of times a year since 2008.

Intelligence professionals -- especially those with a mission as important as the NSA’s -- deserve the benefit of the doubt on many issues. But the alarming behavior the recent leaks have revealed shows that the NSA requires strong supervision, and it’s clear that the current system of oversight is failing.

By law, the NSA is prohibited from snooping on American citizens. Yet its modus operandi -- sweeping up colossal amounts of information on phone calls, e-mails and other electronic communications ostensibly from foreign intelligence targets -- lends itself to doing so inadvertently. The Post revealed an internal NSA audit showing that agents improperly collected and stored troves of data on Americans, retained information they were required to destroy, and failed to report incidents of inappropriate collection. One document appears to instruct analysts in the fine art of stonewalling government overseers.

Under two presidents, the NSA has been found to be exceeding its legal authority, systematically “overcollecting” data and failing to exercise adequate oversight. Its leadership has obfuscated, misled the public and issued statements that now look like something very close to outright lies.

President Barack Obama, in a news conference that sounds a lot worse today than it did last week, asserted that one of the NSA’s programs “is an important tool in our effort to disrupt terrorist plots.” But he offered no evidence, so as with most things involving the NSA, no one has any idea if it’s true. That makes judging the costs and benefits of such programs extremely difficult -- the benefits are entirely secret, but the costs keep piling up in public.

As the president noted, widespread surveillance risks diminishing American moral authority abroad. It’s eroding the traditions of privacy and liberty Americans have long demanded, not to mention treading a very fine constitutional line. And it’s sure to have ugly economic consequences: The technology companies that have acquiesced in the NSA’s snooping shouldn’t be surprised if they’re subjected to far more stringent privacy regulations in other countries or if their products become substantially less popular in a global marketplace.

The president announced last week a number of measures intended to mollify the public. There will be a full-time privacy officer at the NSA, he said. A panel of outside experts will review intelligence collection. There will even be a lively new website “that will serve as a hub for further transparency.”

Increasingly, all this looks like a fool’s game. The system of supervision simply isn’t working. As the Post report notes, the NSA’s oversight staff has quadrupled in recent years, yet the rate of infractions keeps increasing. Even the chief judge of the Foreign Intelligence Surveillance Court -- the secret body putatively in charge of making sure the NSA follows the law -- has admitted that the court can’t verify what the agency says and thus can’t provide full oversight over it.

There’s one branch of the government that can, and that’s Congress. Congressional inquiries are not always the most high-minded affairs. But we’ve reached the point where an expansive, intrusive and transparent investigation -- modeled on that of the Church Committee in the 1970s -- may be the best way to fully protect Americans’ security and privacy. If NSA officials find themselves under uncomfortably public and revealing scrutiny, they’ll have no one to blame but themselves.

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