"I don't know whether or not such collusion - and that's your term - such collusion existed, I don't know," Brennan said.
Brennan also denied that he had made last minute requests to unmask names of any U.S. Persons - possibly linked to the Trump Campaign - before the former CIA Director left the agency as President Trump was sworn into office on January 20, 2017.
The Russia investigation was also grabbing the attention of Senators at the same time, as Director of National Intelligence Dan Coats refused to say whether he had been pressured by the President - or by White House officials - to try to get the FBI to drop its investigation into the Russia matter.
"I don't feel it's appropriate to characterize conversations with the President," Coats said.
A former Senator, Coats seemed ill at ease as he sidestepped the queries of some of his former colleagues.