Late night host Stephen Colbert used a Dr. Seuss-style rhyme to poke fun at President Biden amid concerns about his cognitive health and ability to serve as president. 

Colbert, long one of Biden's most dependable allies in the media, has sharpened his mockery of the president following his debate performance. 

"Is he mentally fit?" Colbert said, reading out of a mock book titled, "Oh The Places For Joe!" 

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Colbert proceeded to read passages from the book, a parody of the Dr. Seuss book published in 1990 called, "Oh, the Places You'll Go!" 

"Can he serve a whole term?" Colbert said. "Can he beat RFK with his brain full of worm? Just ask him, just ask him, the man loves to talk, as long as you ask him before eight o’clock."

"Join Joe Biden as he explores a wonderful world outside of the Oval Office!" the parody book's description reads. 

"Here's the thing," Colbert said. "Maybe Biden can't win. Or maybe he's the only one who can win. I don't know what the right answer is and I'm not alone." 

Just months ago, Colbert participated in a lavish record-setting fundraiser that brought in $26 million for the Biden campaign.

Colbert took the stage in New York City with Democratic presidents Joe Biden, Barack Obama and Bill Clinton to moderate their conversation in March. 

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Colbert is not the only celebrity who has turned on Biden. 

Following a glitzy June 15 event in Los Angeles that reportedly raised over $30 million for Biden's campaign, one of the event's A-list guests, actor George Clooney, has since turned on the president and is calling on him to step down. 

Clooney called on Biden to leave the 2024 race in a New York Times guest essay on Wednesday, writing, "It’s devastating to say it, but the Joe Biden I was with three weeks ago at the fund-raiser was not the Joe ‘big F-ing deal’ Biden of 2010. He wasn’t even the Joe Biden of 2020. He was the same man we all witnessed at the debate."

"This is about age. Nothing more. But also nothing that can be reversed. We are not going to win in November with this president," Clooney wrote. 

The Biden campaign did not immediately respond to a request for comment from Fox News Digital. 

Fox News' Kristine Parks and Brie Stimson contributed to this report.