He didn't take the Fifth. He just said he wouldn't reveal classified information. On the same show, James Clapper make it crystal clear a few minutes later that the President's accusations never happened. He said so flat out.
What he said was that there was no wire tap of trump, or trump campaign aids being wire tapped, and then said there was no wire tapping of Trump tower.
What he did not say, is that there was no FISA warrant for the surveillance of the Russian bank or banks that were communicating with a trump owned server, NOT LOCATED IN Trump tower.
There are two articles from Slate on Computer scientists say a Russian Bank is secretly communicating with a Trump server secretly..... Google it....
Well, in one of the two related articles, it states that it turns out, this trump server WAS NOT LOCATED in Trump tower as they had thought, but they traced its location to a Computer service company, hired by Trump to service and maintain it.
So that leaves open that the FISA warrant f r surveillance of the Russian bank or banks that was secretly communicating with TRUMPs server could still be out there even with Clappers statement being the truth.