That sort of speculation is the foundation of the right wing echo chamber. A report of literally nothing becomes a conspiracy by Obama and Soros to spy on Trump. Dovetails nicely into things like Trump Tower being bugged (false) or other such right wing garbage.
I'm saying its an odd thing to do, especially from Dershowitz. Go to super right wing media and say you know of this but you can't reveal any of it. You target the readerships' two biggest lightning rods for hate and wackadoodle conspiracy nuts -- Obama and Soros- and you literally offer no substance whatsoever. Why do that? Just really odd, especially for him.