Yeah, just remember back a few years ago, the head of the NSA testifying that nope, no Americans were being spied on. And the Senators kept trying to get him to answer the truth, they knew it from their classified briefings, but he was comfortable lying in public.
Took Snowden to reveal that he was lying his fucking ass off. I fully expect we'll be relying on a similar brave move to crack this open.
Anything embarrassing might be used by our enemies to humiliate us! Therefore, have to keep it secret.