Has the NSA gone rogue?

President Obama has had to answer reports that the U.S. monitored German Chancellor Angela Merkel's cell phone.

• Evidence indicates that the NSA stores contents of phone conversations and e-mails


• NSA can investigate only when it can show reason it might be linked to foreign threat


• Christopher Slobogin: If it is monitoring many thousands of calls, are all those justified?


• Slobogin: Congress must make sure the NSA abides by the laws it has enacted

Editor's note: Christopher Slobogin, who holds Vanderbilt Law School's Milton R. Underwood Chair in Law, is the author of "Privacy at Risk: The New Government Surveillance and the Fourth Amendment."

(CNN) -- The National Security Agency scandal keeps getting juicier. Recent revelations, triggered by ex-NSA employee Eric Snowden's earlier disclosures, indicate that the National Security Agency not only collects volumes of metadata about the phone numbers people use, it routinely stores the contents of phone conversations, text messages, e-mails and Internet activity.

Former Vice President Dick Cheney explains that the collection of all of this information is crucial, because NSA staffers cannot know what bits of it will turn out to be relevant to a counterterrorist investigation.

In fact, the Foreign Intelligence Surveillance Court has agreed with that argument in approving bulk collection of American as well as foreign metadata for the past seven years. And if metadata must be stored for this purpose, it is an easy step from there to conclude that the contents of communications must be stored as well.

The key question then becomes when the NSA may "query" or identify the source of the metadata it has stored and read the communications it has collected. The NSA reports that it conducts queries of metadata only when it has a "reasonable, articulable" suspicion that a number is linked to a foreign threat that has been identified as such by the Foreign Intelligence Surveillance Court. Section 703 of the Patriot Act, as amended in 2008, limits looking at the contents of a communication to situations where the court has found probable cause to believe that information about a foreign threat will be revealed.

Glenn Greenwald on NSA spying on allies

Spy Directors fire back on Capitol Hill

NSA chief: Europeans shared data

Although one could ask for more oversight, this isn't a bad set of legal safeguards. If they were followed, the European naysayers about the NSA's exploits would not be so hot under the collar.

Many countries besides the United States collect and analyze electronic communications for national security purposes. The Wall Street Journal reported Wednesday that France and Spain helped our surveillance efforts by handing over phone records they collected on their citizens. Illustrated by the ease with which this spying took place, these countries impose fewer limitations on their surveillance activities than we do.

The real question is whether we follow those limitations. Although the NSA may not conduct queries or examine content unless it or a court determines that "national security" is at stake, national security is apparently at stake quite often, if the recent reports about monitoring hundreds of thousands of foreigners' calls as well as the calls of foreign leaders are true.

American journalist Glenn Greenwald, the principal conduit for Snowden's revelations, even claims that the NSA is as interested in economic intelligence as it is in exposing terrorist plots. He offers as evidence documents showing that the U.S. has spied on conferences about negotiating economic agreements and on oil companies and ministries that oversee mines and energy resources.

This may be the real reason European leaders are so incensed. Surveillance of terrorists is fine and probably can help them quite a bit. But surveillance of politicians and capitalists crosses boundaries that they might think should not be crossed, at least unless and until their intelligence agencies can do it as well as and as often as the U.S. can.

In the meantime, Congress should get serious about making sure the NSA abides by the laws it has enacted.

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The opinions expressed in this commentary are solely those of Christopher Slobogin.

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