Clinton campaign manager John Podesta refused to confirm the legitimacy of a hacked email published by WikiLeaks in which he called Bernie Sanders a "doofus," but did admit he was "frustrated" with the progressive senator for opposing a 2015 climate change deal.

"Well, you know, I have great respect for Bernie Sanders," he said when asked about the email on CNN. "There was a moment where he opposed the Paris deal, where, you know, without confirming the accuracy of the email, I was frustrated with him, but he and I have a very good relationship… I didn't think he was taking the right position and I'm very proud of president Obama for delivering such an important climate agreement."

Sanders argued the day before the agreement was reached in December 2015 it didn't go far enough, asserting that the "planet is in crisis. We need bold action in the very near future and this does not provide that." According to an email obtained by WikiLeaks, Podesta wrote "Can you believe that doofus Bernie Sanders attacked it?" the day the language of the international greenhouse gas reduction deal was reached.

"I'll take that as a yes," CNN host Wolf Blitzer said in response to Podesta.

"I'd take that as a statement that I have grade admiration for Senator Sanders," Podesta shot back.

He also said that "even members of the CNN crew" might regret what they say privately. "I know, we know. Got to be careful with your emails then," Blitzer said.