I can't help but feel that this is fake outrage, given for example, this writeup of a 60 minutes interview ... from the year 2000: http://www.cbsnews.com/news/ex-snoop-confirms-echelon-networ... "America politicians may also have been eavesdropped on, says Margaret Newsham, a woman who worked at Menwith Hill in England, the NSA's largest spy station. She says she was shocked to hear the voice of U.S. Sen. Strom Thurm…
This is why the question is such a good one. When 'Snowden's grandmother' tried to out them on exactly this minor detail of spying on a congressman she did not provide any primary first hand evidence, e.g. a tape recording. It was her word against the NSA's. Obviously we believe her, or at least we do now!
So when the NSA say they have never spied on anyone in congress, they will have to carefully craft their lie. I can't wait for it!