“Garrow is confident the information is accurate.”
I believe it to be true...I heard about it contemporaneously from FBI and DEA agents with whom I worked at the time.
I remember Paul Ryan commenting about all the rumors and allegations he had heard from "reliable" sources about Trump's cooperation and collusion with the Russians. Ryan of course was "deeply concerned" and convinced of their truth.
Washington DC is worse than a high school lunchroom in terms of transmitting, warping and believing lies and rumors. I imagine that was a major part of Brennan and Clapper's plan all along. The idea that "high placed sources" told you something carries zero weight.