(NewsNation) — President Joe Biden and former President Donald Trump squared off in a heated first presidential debate of the 2024 election filled with notable moments, including questions about their age, fitness to serve and cognitive ability.

At times, Biden struggled to finish his sentences or complete a talking point before trying to move on.

He was also reminded by CNN moderators Jake Tapper and Dana Bash to use the rest of his time when he cut his answers and responses to Trump short.

Biden’s debate performance under microscope

Early in the debate, Biden appeared to lose his train of thought while answering a question about the national debt. He started by saying Trump increased the national debt and blamed tax cuts on the wealthy for America’s economic woes.

“Child care, elder care, making sure that we continue to strengthen our health care system, making sure that we’re able to make every single solitary person eligible for what I’ve been able to do with the, uh, with the COVID. Excuse me, with dealing with everything we have to do with … look, if we finally beat Medicare.”

Neurologist Dr. Tom Pitts explained to “Morning in America” that viewers observed a moment of “word-finding difficulty in action.”

“When you talk about Biden’s issue there, that is not really per se confusion at that moment,” he said.

Pitts went on to describe how as people age, the brain’s left frontal temporal area degenerates. When people see something, their brain puts out the first five or 10 things. For example, in a furry animal, someone might say “cat, cheetah, tiger, leopard” until they pick the correct one.

“In this setting, when you can’t get there, you pick a close thing. So, if you saw a cheetah, you might call it a lion,” he said. “That’s why he came up with ‘we beat Medicare.’ That’s not what he was thinking or wanted to say, but that’s what happens with progressive kind of aphasias and degeneration of word-finding difficulties.”

Did a cold impact Biden’s performance?

The president’s voice was often raspy, which the White House later attributed to a cold, and he at times lost his train of thought or struggled to make his point clearly.

Pitts said that whether Biden had a cold or not wouldn’t impact his performance.

“You see monotone, hypomania and degenerative diseases like parkinsonism and Alzheimer’s — people become more monotone and soft like that. That’s one of the first indicators I have when people don’t have tremors in parkinsonism or Alzheimer’s, is a soft monotone voice. We also see smaller handwriting as well, that has to do with degeneration of the brain, nothing to do with a cold”

Biden on performance: ‘We did well’

Biden brushed off concerns about his debate performance against Trump Thursday despite widespread panic among Democrats about how the night played out.

He took a few questions from reporters after placing an order at a Waffle House in Atlanta following the debate.

“I think we did well,” Biden said.

Vice President Kamala Harris defended Biden’s debate performance during a round of interviews on Thursday night, even as she conceded he had a “slow start.”

“Yes, there was a slow start, but it was a strong finish,” she said on CNN. “And what became very clear through the course of the night is that Joe Biden is fighting on behalf of the American people.”

Is Trump up for the job?

Both Biden, 81, and Trump, 78, would be the oldest person ever elected president in history if they win in November. 

When asked about his capabilities to be reelected, Trump expressed no concerns over his age and said that he “aced” two cognitive tests.

“I took two cognitive tests, I took physical exams every year,” Trump said. “I’m in very good health.”

Pitts explained that the Montreal Cognitive Assessment, which Trump referenced, is a screening test. Passing it indicates that a person does not have dementia, while failing it suggests a person is “massively impaired,” he said.

He noted that Trump fares better cognitively than Biden, but expressed concerns about Trump’s “narcissism and perpetual lying essentially and an exaggeration,” which fall into a realm of personality disorders.

Trump also said he would “like to see” Biden take a cognitive test, and continued to poke fun at Biden’s mental faculties, as he has previously done in a campaign ad.

If Trump were elected in November, he’d be 82 at the end of his term. If Biden were elected in November, he’d be 86 at the end of his term.

NewsNation’s digital producer Liz Jassin, digital intern Isabelle Charboneau and The Hill contributed to this report.