Editor's Note: On July 6, the Washington Post published a story based off of Edward Snowden's cache that shows most of people caught in the National Security Agency's survillence net are ordinary Internet users, not legally targeted foreigners. That's happening thanks to Section 702 of the Foreign Intelligence Survillence Act, the very "backdoor" discussed here.

On June 20, the House of Representatives passed a defense spending bill with an amendment that would substantially strengthen the privacy protections of American citizens in the context of foreign intelligence surveillance. The amendment, which passed by an overwhelming bipartisan vote of 293-123, should be quickly and enthusiastically approved by the Senate and then signed into law by President Obama.

Complicating matters, the Privacy and Civil Liberties Oversight Board, which makes recommendations to Congress about such matters, just issued a deeply disappointing report that does not go as far as the House’s enactment. That report is simply wrong, and should be rejected. Let me explain.

Most of the focus in the United States about National Security Agency surveillance programs has been on the section 215 telephone metadata program, which directly involves the collection of phone records of American citizens. The vast majority of NSA foreign intelligence programs, however, are directed at people who are not U.S. citizens and who are not in the United States. They are directed, in short, at potential foreign terrorists.

Because of the Fourth Amendment and the Foreign Intelligence Surveillance Act (FISA) of 1978, when an individual is present inside the United States, the government is not permitted to search his home, open his mail, wiretap his phone, or read his emails without first obtaining a warrant from a judge based on a finding by the judge that there is probable cause to believe that the intrusion on personal privacy is likely to reveal information relevant to a criminal or foreign intelligence investigation. That same rule applies when the government wants to investigate an American citizen who is outside the United States. In that case, the NSA must first obtain a warrant from a judge on the Foreign Intelligence Surveillance Court.

On the other hand, under section 702 of FISA, if the person being investigated is not an American citizen and is reasonably believed to be located outside the United States, the NSA can intercept and collect his communications if the NSA finds that there are reasonable grounds to believe that the target’s communications might contain information relevant to international terrorism. It doesn’t need a warrant.

The lower standard for surveillance of individuals in this situation is justified on the ground that a nation has special obligations to its own citizens that it does not necessarily owe to citizens of other nations. The analogy is to a family, which has responsibilities to family members that are different from its responsibilities to persons outside the family. Every nation follows this approach. There are, of course, good reasons to respect the privacy rights of citizens of other nations, both in terms of basic human rights and in terms of our own national self-interest, and it may be that the authority given to the NSA to intercept and collect the communications of non-Americans who are outside the United States should be reconsidered. But that is a subject for another day.

Here’s the problem: When the NSA uses section 702 to collect the communications of suspected foreign terrorists outside the United States, it will sometimes inadvertently pick up the communications of American citizens.

This might happen is one of two ways. First, even though the NSA has “reasonable grounds to believe” that the target is a non-American, it will sometimes be wrong. On occasion, the target will in fact turn out to be an American citizen. But that person’s emails, phone calls, etc. will now be contained in the NSA’s database. Second, even if the target is, in fact, a non-American, the target will sometimes be emailing or calling an American citizen. In that situation, the American citizen’s communications with the target will be incidentally picked up by the NSA, and they too will wind up in the NSA’s database.

Assuming that the NSA’s collection of these communications is authorized by section 702 and is both lawful and constitutional with respect to persons who are not American citizens, what rights, if any, do American citizens have in the privacy of their communications when those communications have incidentally been intercepted and collected by the NSA? This raises the issue of so-called “backdoor” searches. That is, once the NSA has these communications in its database, can it then lawfully search the database for the communications of American citizens?

The defenders of backdoor searches maintain that, because the initial interception and collection of the communication was lawful, the government is free to use the information obtained against anyone. This is, indeed, the general approach to searches in the United States. For example, if the government lawfully (with probable cause and a warrant) reads X’s emails or wiretaps X’s phone calls, and it learns from X’s emails or phone calls that Y is engaged in illegal activity, it can legally use that information against Y, even though the government had no legal justification to intercept Y’s communications. Because the interceptions were themselves lawful, the general rule is that the government can use the lawfully obtained information against anyone, including Y. The defenders of backdoor searches argue that the same rule should apply in the section 702 situation.

Last fall, I served on a five-member Review Group that was charged by the president with making recommendations about reforming the nation’s foreign intelligence programs. [Our report is here: (PDF)] After reviewing this issue, we recommended that the law should be changed as follows: “The government may not search the contents of communications acquired under section 702… in an effort to identify communications of particular United States persons, except… when the government obtains a warrant based on probable cause to believe that the United States person is planning or is engaged in acts of international terrorism.”

In effect, the Review Group recommended that backdoor searches for communications involving American citizens should be prohibited unless the government has probable cause and a warrant. This is essentially what the recently enacted House amendment endorsed.

The Review Group concluded that the situation under section 702 is distinguishable from the situation when the government lawfully intercepts a communication when it has probable cause and a warrant. This is so because, in the section 702 situation, the government is not required to have either probable cause or a warrant to intercept the communication. Because section 702 was not intended to enable the government to intercept the communications of American citizens, because our recommended reform would leave the government free to use section 702 to obtain the types of information it was designed and intended to acquire—the communications of non-U.S. citizens, and because the recommended reform would substantially reduce the temptation the government might otherwise have to use section 702 impermissibly in an effort intentionally to intercept the communications of American citizens, we concluded that this reform was both wise and essential.

Now that the House of Representatives has agreed, it is time for the Senate and the president to move forward to make this recommendation a reality. This change would be an important step forward in our nation’s effort to strike the right balance between liberty and security in a changing world.