US Congress to NSA: How many Americans do you illegally spy on?

NSA: It's hard to tell. Now could you reauthorize our authority to keep doing it?

If there is one piece of information that would fatally undermine the NSA's argument that it doesn't abuse Section 702 of the Foreign Intelligence Surveillance Act (FISA), it would be the number of American citizens whose personal information it has "incidentally" hoovered up."