It's not just a handful of congressional Democrats who are urging U.S. President Joe Biden to re-think his re-election prospects — some prominent party supporters and donors are, too.

The 81-year-old Biden has been fighting to keep his re-election effort afloat after a much-criticized June 27 debate performance against 78-year-old Donald Trump, the presumptive Republican nominee for president. The two men are the two oldest candidates to seek the presidency.

On Wednesday, Hollywood actor George Clooney publicly joined the chorus of voices calling for Biden to quit the presidential race.

In an op-ed published in the New York Times on Wednesday, Clooney withdrew his support for Biden, saying the Democrat leader was not the same man he was in 2020.

WATCH | Vanity Fair's Brian Stelter on Democrats' concerns: 

George Clooney says Joe Biden should quit presidential race

Movie star George Clooney adds his voice to those of Democrats calling for President Joe Biden to step aside. The CBC's Katie Simpson brings us up to speed on the latest fractures in the Democratic Party. Plus, special correspondent to Vanity Fair Brian Stelter tells us why he thinks the Democratic Party is in 'a state of suspended animation.'

"It's devastating to say it, but the Joe Biden I was with three weeks ago at the fundraiser 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," Clooney, who recently co-hosted a fundraiser for Biden, wrote in the op-ed.

"We are not going to win in November with this president. On top of that, we won't win the House, and we're going to lose the Senate."

Biden defying calls to go

Since the debate, Biden has defied calls to exit the ballot and given interviews to ABC News and MSNBC's Morning Joe to drive home the message he's ready to fight Trump for the presidency this November.

But he's still fighting growing pushback to being the Democrats' contender — including from eight House Democrats who have publicly said Biden must go.

Brian Stelter, a special correspondent for Vanity Fair, said it's unlikely that Biden is going to see less of this type of criticism with time.

"This is a drum beat that is going to continue," he told CBC's Power & Politics on Wednesday.

Clooney's call for Biden to back out follow calls from other prominent Democrats, including those from show business.

Actor and director Rob Reiner said in a social media post Wednesday that Clooney had "clearly expressed what many of us have been saying."

Reiner, who had already called for Biden to drop out, renewed that call on Wednesday.

Damon Lindelof, the co-creator of the TV series Lost, last week called for Democrat donors to withhold funds until Biden is off the presidential ticket.

Comparing Biden to a tired baseball pitcher who needs to be pulled off the mound, the screenwriter said he's "ready to hear the walkout song for our closer," in his guest column published by the website Deadline.

Activist and filmmaker Abigail Disney has also called for Biden to end his re-election bid. 

WATCH | How the Democrats could choose another candidate: 

3 ways the Democrats could replace Joe Biden | About That

As a growing number of Democrats call for Joe Biden to drop out of the 2024 U.S. presidential race ahead of the Democratic National Convention, About That producer Lauren Bird breaks down the options to replace him on the ballot and what makes some of them especially challenging.