In the past 48 hours, the American public has been rocked by revelations about the scope of domestic government surveillance. First, we learned that the National Security Agency receives information about the majority of domestic and international phone calls placed in this country. Then we discovered that the NSA and FBI collaborate to vacuum up real-time information from the servers of most major Internet companies as well, including the content of emails, video chats, documents, and more. Although this program is ostensibly directed at gathering data about foreigners, it is likely to sweep in significant amounts of information about Americans too.

There are, needless to say, significant privacy and civil-liberties concerns here. But there’s another major problem, too: This kind of dragnet-style data capture simply doesn’t keep us safe.

First, intelligence and law enforcement agencies are increasingly drowning in data; the more that comes in, the harder it is to stay afloat. Most recently, the failure of the intelligence community to intercept the 2009 “underwear bomber” was blamed in large part on a surfeit of information: according to an official White House review, a significant amount of critical information was “embedded in a large volume of other data.” Similarly, the independent investigation of the alleged shootings by U.S. Army Major Nidal Hasan at Fort Hood concluded that the “crushing volume” of information was one of the factors that hampered the FBI’s analysis before the attack.

Multiple security officials have echoed this assessment. As one veteran CIA agent told The Washington Post in 2010, “The problem is that the system is clogged with information. Most of it isn't of interest, but people are afraid not to put it in.” A former Department of Homeland Security official told a Senate subcommittee that there was “a lot of data clogging the system with no value.” Even former Defense Secretary Robert Gates acknowledged that “we’ve built tremendous capability, but do we have more than we need?” And the NSA itself was brought to a grinding halt before 9/11 by the “torrent of data” pouring into the system, leaving the agency “brain-dead” for half a week and “[unable] to process information,” as its then-director Gen. Michael Hayden publicly acknowledged.

Data mining is good at finding credit card fraud. It's not so good against terrorism.

National security hawks say there’s a simple answer to this glut: data mining. The NSA has apparently described its computer systems as having the ability to “manipulate and analyze huge volumes of data at mind-boggling speeds.” Could those systems pore through this information trove to come up with unassailable patterns of terrorist activity? The Department of Defense and security experts have concluded that the answer is no: There is simply no known way to effectively anticipate terrorist threats.