Nadler seemed pretty sure on Thursday at the Committee meeting and when interviewed by CNET over the weekend but has now changed his story. The NSA released a very strangely worded denial. And in today's Q&A Snowden says this is exactly how it happens.
Not sure what to make of all this but is seems like we have been given a peek behind the curtain but not a long enough gaze to see exactly what is going on.
Regardless, I think the implication that somebody must have "gotten to" Congressman Nadler and therefore we should continue to believe what we thought he said earlier rather than what he's saying unambiguously now is totally ridiculous.
[0] http://www.c-spanvideo.org/clip/4456140 (it's right near the start).
For what it's worth, from what I've seen of Rep. Nadler in the past, he doesn't seem like the kind of craven politician who would either equivocate or be scared into submission.
For the rest, I don't see how it's possible to prove the negative: that the NSA isn't doing what you claim in your piece... but if the only evidence they are is second-hand from what Rep. Nadler says he heard in a secret hearing... and now he says he was wrong... Well, seems awfully weak to me.