Democrats are privately "panicking" over Pennsylvania Senate candidate John Fetterman's debate performance Tuesday night and expressing regret over his decision to debate Republican opponent Dr. Mehmet Oz, according to NBC.

The Democrat's lingering health problems due to a stroke he suffered in May resulted in a debate performance that some said was "painful to watch." Some Democrats felt Fetterman hadn't been transparent about the degree of his speaking difficulties and criticized his campaign for agreeing to the one and only debate.

"[F]ellow Democrats are second-guessing his decision to appear on stage five months after a stroke — and some question whether he should have remained on the ballot at all," the NBC article began. 

John Fetterman debates Dr. Mehmet Oz

Democratic Senate candidate John Fetterman participates in a debate with his GOP challenger Dr. Mehmet Oz in Harrisburg, Pennsylvania, on Tuesday. (NewsNation)

Chris Kofinis, a veteran Democratic campaign strategist, put it bluntly to NBC: "He should not have debated. Anyone on his team who agreed to a debate should be fired, or never work again, because that debate may have tanked his campaign."

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Several Democrats were apparently "shocked" by the extent of Fetterman's speaking difficulties during the debate, leaving some Democrats to question why he was still running.

One senior Senate Democratic aide told NBC they found Fetterman's performance "startling."

"I really question the judgment that he continued with this race," the person said.

"Folks are pretty much freaking out on the Dem side," Khari Mosley, a Pittsburgh-based Democratic consultant and grassroots activist added.

A close photo of John Fetterman

Fetterman has lingering health problems due to a stroke he suffered in May. (AP Photo/Gene J. Puskar, File)

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Others blasted the Fetterman campaign for agreeing to only four nationally televised interviews up until a few weeks ago.

"Their team has been ignoring what tons of strategists and insiders have been saying for months: We’ve expressed our concerns many, many times about being more transparent," the anonymous source told NBC.

The outlet reported that Fetterman had declined "multiple requests" from NBC News and other media outlets to release his complete medical records.

Reporter calls out Fetterman's health issues

An NBC reporter was blasted for her comments about interviewing Fetterman. (Fox News)

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Terry Madonna, a longtime Pennsylvania pollster, didn't mince words when describing the debate.

Describing the backlash, Madonna said, "[T]he fact of the matter is his performance was obviously very questionable and it’s just dominated the news."

He added that he’s never seen a debate performance "this bad," the NBC article read.

Fetterman's debate drew strong reaction on the left. Some pointed the finger at his campaign, while others claimed his critics were "ableist."