CBS late-night host Stephen Colbert found himself at odds with former Biden Press Sec. Karine Jean-Pierre when she trashed the Democrat Party on Monday and said she never saw any indication of Joe Biden’s mental decline.

Colbert was argumentative with the former press secretary when she insisted she didn’t see Biden decline during her tenure in his administration and he pushed back, saying that Biden’s performance at the single presidential debate against Donald Trump was very concerning.

“No one is saying that he didn’t age,” Jean-Pierre exclaimed. “I’m talking about did he have… the mental acuity, was he able to govern? And the man that I saw nearly every day was someone who was engaging, understood policy, and was always putting the American people first.”

But Colbert was not convinced by Jean-Pierre’s claim that Biden was just fine.

“It was very personal for those of us who watched [the debate] too, because it was a shock to our system to see that. Because — I mean, you’re talking to a guy who helped raise $25 million for Joe Biden in March of that same year,” he told Jean-Pierre. “And three months later, I saw a guy who I had not seen backstage at the benefit that I did. It seemed like a dramatically different person. And at 81 years old, that’s not entirely unexpected. You can imagine why people got so worried.

“I don’t think anybody questioned his heart or his policies. But it takes more than that to be the President of the United States,” Colbert added. “And in a moment of great pressure on stage, we saw someone shock us and worry us, and nothing could assuage that worry. So I don’t think it was necessarily a betrayal of Joe Biden as other people saying, ‘We don’t think we were shown the Joe Biden that you saw.'”

Jean-Pierre insisted that the criticisms of Biden and the demands that he step down were a “really ugly assault on someone who had 50-plus years of experience and who, again, objectively had done a good job as President of the United States.”

She added that “it was heartbreaking to see that type of behavior.”

“Disappointment is such a light term,” Colbert replied. “It was harrowing. OK, look, listen, we are never going to agree on this other than the fact that I’m glad that you came here tonight.”

In her book, Jean-Pierre said that she was so upset by the demand that Biden step down and back out from running for reelection, she has decided to leave the Democrat Party.

“Now the cloud of unease hovering over me solidified into an idea about how I could possibly do something different. How I could channel my disappointment into some kind of concrete action that would allow me to fight for what I believed in without giving blind loyalty to a party I felt no longer deserved it,” she wrote.

“You know what? I’m going to become an independent. I don’t think I can stomach being in the Democratic Party anymore,” she added.

In a separate interview, she told CBS Mornings hosts that Biden was sharp and able to govern.

But host Tony Dokoupil expressed skepticism over her claims.

“I have to say, I thought you were going to say that, try as you might to convince Joe Biden to drop out of the race — because what we were seeing is what you were seeing, and he was struggling, and couldn’t do it — I thought you were going to say you were angry at that,” Dokoupil said to Jean-Pierre. “What you said in this book is you’re angry at the people who tried to push him out.”

“Some Americans are going to say, ‘seriously?’” Dokoupil added.

Co-host Gayle King agreed and said she was highly skeptical that Biden’s associates could not see his decline.

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