The former director of the Central Intelligence Agency said Americans should be worried whether the president of the United States is a madman.
John Brennan appeared on MSNBC's "The Last Word" with Lawrence O'Donnell on Wednesday.
"President Donald Trump's former personal attorney Michael Cohen, in testimony that's he's preparing for Congress next month, will call the president of the United States a madman," O'Donnell noted.
"I think it is corroboration for what a lot of people have believed for so long," Brennan noted. "A belief that has been born out by a lot of Mr. Trump's actions and policies and statements over the last two years."
"But I think more than that, it's very worrisome that this is the person that American citizens entrust with their national security, with their future prosperity," he added.
"It's very, very worrisome, because he is in the Oval Office, he's the incumbent right now," he warned. "And we all should be very worried about his lack of stability."
O'Donnell asked Brennan about reports Trump attempted to conceal his conversations with Russian President Vladimir Putin from his entire administration.
"I've never encountered a situation like this before, because the previous presidents that I've worked for, both Democrat and Republican, would want to make sure that senior staff and directors of intelligence agencies would want to understand because that gives us a sense how the Russians might try to exploit whatever was discussed there," he explained.
"So it's inexplicable why Mr. Trump did not allow his National Security Adviser and Secretary of State in that meeting," he said.
"Clearly he was trying to keep something from them," Brennan concluded. "What was he concealing? And what did Mr. Putin come away with from that conversation?"