One Possible Answer

The Conservative Treehouse site states their bias in their name - refreshing. Nevertheless, they have a very short take on what Nunes saw and why he saw it at the White House. Check it out.

The “tipster” source is unknown. However, the actual intelligence report(s) he reviewed, which contained the unmasked surveillance information, was simply President Obama’s daily intelligence Briefing(s).

It appears, most likely, someone (aka mysterious tipster), simply told Nunes which dates to review. Hence the Executive Branch SCIF was utilized. The ACTUAL intelligence product itself was the Executive Office Presidential Daily Intelligence Briefing.

Most likely a Clapper (ODNI), Rogers (NSA), Comey (FBI Counter Intel), and Brennan (CIA) work product. Remember, President Obama preferred written intel briefings which he reviewed from his secure iPad.

Is this true? I have no idea. Is it plausible? Definitely. If it is true, you have to wonder why Sean Spicer hasn't splashed it all over the WH press briefing. Difficulties getting it declassified, one supposes. Hat tip to Lucianne.com for the link.