The National Security Agency's (NSA) Inspector General explains that he cannot provide an estimate of how many Americans the agency has spied on, because doing so "would itself violate the privacy of U.S. persons."

Inspector General I. Charles McCullough concludes his letter by claiming that he "firmly [believes] that oversight of intelligence collection is a proper function of an Inspector General," adding that he will "continue to work with you and the Committee to identify ways that we can enhance our ability to conduct effective oversight."

While it's not surprising that an NSA official would simply refuse to respond to any and all questions from Congress -- they typically do -- it is unusual for the agency to claim that a basic oversight function like estimating how many Americans have been spied on is effectively too great a task for them to even attempt, and may actually be beyond the purview of the Inspector General.

"All that Senator Udall and I are asking for is a ballpark estimate of how many Americans have been monitored under this law, and it is disappointing that the Inspectors General cannot provide it," Wyden told Ackerman. "If no one will even estimate how many Americans have had their communications collected under this law then it is all the more important that Congress act to close the 'back door searches' loophole, to keep the government from searching for Americans' phone calls and emails without a warrant."