Trey Gowdy asked Brennan if unmasking was requested by an ambassador. Brennan was clearly not expecting this question and fumbled an answer. I saw this response on twitter but can’t find it at the moment. Obviously Gowdy already knew about Powers.
In the closed caption "transcript," scroll down to 01:45:49 Gowdy and 01:47:03 Brennan
May 23, 2017 Mr. Trey Gowdy asking Brennan about Unmasking Critical nature of protecting identities; ... DO YOU RECALL ANY U.S. AMBASSADORS ASKING THAT THE NAMES BE UNMASKED?
You're right. I just posted in another reply that the question knocked Brennan back on his heels. He clearly wasn't expecting it and his face looked like "oh crap...what does this guy know'? He didn't know the answer to his own question so he lied without technically lying. He said it may be ringing some bells in the back of his mind but at this time he couldn't remember. Yeah right!