CNN national-security analyst Peter Bergen argues that the NSA, CIA, and FBI had all the information they needed to prevent 9/11, but the Bush Administration failed to follow through. Providing more tools to the NSA would do nothing except give them more power:
The government missed multiple opportunities to catch al Qaeda hijacker Khalid al-Mihdhar when he was living in San Diego for a year and a half in the run up to 9/11, not because it lacked access to all Americans phone records but because it didn't share the information it already possessed about the soon-to-be hijacker within other branches of the government.
The CIA also did not alert the FBI about the identities of the suspected terrorists so that the bureau could look for them once they were inside the United States.
These multiple missed opportunities challenge the administration's claims that the NSA's bulk phone data surveillance program could have prevented the 9/11 attacks. The key problem was one of information sharing, not the lack of information.
Since we can't run history backward, all we can say with certainty is that it is an indisputable fact that the proper sharing of intelligence by the CIA with other agencies about al-Mihdhar may well have derailed the 9/11 plot. And it is merely an untestable hypothesis that if the NSA bulk phone collection program had been in place at the time that it might have helped to find the soon-to-be-hijackers in San Diego.
Indeed, the overall problem for U.S. counterterrorism officials is not that they don't gather enough information from the bulk surveillance of American phone data but that they don't sufficiently understand or widely share the information they already possess that is derived from conventional law enforcement and intelligence techniques.
The blanket Hoovering up of data by the NSA threatens everyone's liberties. But that cost isn't worth the results by any measure, since the NSA isn't actually making us safer. Their arguments to fear don't change the existing evidence.