As the dust settled over Tuesday night’s sole televised debate in the crucial US Senate race in Pennsylvania, pundits were starkly divided over the impact of the Democrat John Fetterman’s struggles with speech in his recovery from a stroke.

The Pennsylvania lieutenant governor raised the issue of his auditory processing disorder, which makes it difficult for him to understand certain spoken words, in his opening remarks in the debate with his Republican rival, the former TV doctor Mehmet Oz.

“Let’s also talk about the elephant in the room – I had a stroke,” Fetterman said.

Fetterman used closed captioning to help deal with his speech difficulties. Questions and answers were transcribed in real time and beamed through large screens in front of both candidates.

Reporters present in Harrisburg, Pennsylvania, noted that Fetterman occasionally struggled to articulate his views in the hour-long debate. The Philadelphia Inquirer said that he “spoke haltingly and at times mixed up his words”, remarking that “his speaking has been much smoother in stump speeches on the campaign trail and in a recent interview with the Inquirer than during the back-and-forth” of the debate with Oz.

Rightwing news outlets and commentators were much harsher, with several calling for Fetterman to drop out of the race. John Podhoretz, a conservative columnist with the New York Post, described the Democratic candidate as “impaired” and said “it is an act of personal, political, and ideological malpractice that Fetterman is still contesting for the Senate”.

Tucker Carlson, the far-right Fox News host, portrayed the evening as a “full-blown 30-car Amtrak derailment for Fetterman. If that guy’s elected senator from the state of Pennsylvania, you’ll have real concerns about the system being legitimate.”

Pat Toomey, the sitting Republican senator whose retirement opened up the current contest, tweeted that was “sad to see John Fetterman struggling so much. He should take more time to allow himself to fully recover.”

The Fetterman campaign said it had raised $1m on the back of the debate, suggesting a more empathetic response from Democratic donors. Fetterman’s campaign manager, Brendan McPhillips, said the surge in funding indicated that “the people of Pennsylvania have John’s back in this race. They stepped up tonight with a gigantic show of support for John and his debate performance.”

Joe Cavello, Fetterman’s spokesperson, told reporters the candidate had been forced to work off “delayed captions filled with errors”. The company responsible for setting up the captioning system, Nexstar Media, disputed that, saying in a statement the process “functioned as expected”.

Several commentators lauded Fetterman for his courage.

“What John Fetterman is doing right now in the midst of his recovery – so publicly, on the same stage as a smirking TV doctor – is remarkably brave,” said the writer Pat Cunnane.

The Pennsylvania contest is exceptionally fraught given its high stakes. Who wins the race could determine whether the Democrats hang on to the Senate, which is currently split 50-50, or whether the Republicans retrieve it, providing a platform from which to undermine Joe Biden’s agenda.

The Real Clear Politics poll tracker shows Oz steadily closing on Fetterman since August, when the Democrat commanded a nine-point lead. On Wednesday Fetterman had just a 1.3% lead, well within the margin of error.

Fetterman had a stroke four days before the primary in May and required hospital treatment. He released a report from his doctor last week that said he had “no work restrictions and can work full duty in public office”.

Fetterman was asked during the debate whether he would release the full medical report concerning his stroke in the interests of transparency.

“For me transparency is about showing up, I’m here today to have a debate,” he said.

Fetterman’s struggles with speech have become an unexpected and unpredictable factor in a race otherwise dominated by issues such as inflation, abortion and Oz’s record as an election denier endorsed by Donald Trump. But the TV doctor’s controversial stance on his opponent’s medical struggle also amounts to a high-risk strategy for the Republican.

Oz, a former heart surgeon who was turned into a celebrity by Oprah Winfrey, has repeatedly mocked Fetterman for his disabilities. At one point in the debate, Oz said: “Obviously I wasn’t clear enough for you to understand this.”

In previous interventions, the Oz campaign has been openly snarky.

“Dr Oz promises not to intentionally hurt John’s feelings at any point,” the campaign once said.

When Fetterman ridiculed Oz’s complaint about the price of “crudités”, a Republican senior adviser retorted: “If John Fetterman had ever eaten a vegetable in his life, then maybe he wouldn’t have had a major stroke.”