GEOFF BENNETT: While much of the focus is on President Biden right now, there are concerns around the age of both Biden and former President Donald Trump.

Many of those questions have focused on cognitive skills, memory lapses and how they speak in public.

Stephanie Sy looks at some of those concerns.

STEPHANIE SY: Geoff, polls show that Americans have been concerned about this throughout the campaign.

The numbers have been worse for President Biden.

Polls have shown up to 80 percent of voters think he's too old to serve another term.

For former President Trump, up to 56 percent of voters say he's too old for the job.

We spoke to a couple of older voters with different perspectives this week.

ROBERT TERRY, Massachusetts Resident: I admire Biden for what he has done and what he is.

But, see, my age is 93 -- 92, by the way.

And I guess I had to be concerned.

During the debate, it seemed fairly clear to me that he was having some difficulties from time to time.

Despite the fact that I sympathize with President Biden and his health, the fact is, just like me, he's not getting any younger.

KARL KINDEL, Washington, D.C., Resident: He may talk slow, he may stutter, he may walk slow, but he does know what he's doing.

And he is -- knows enough that he's getting good staff to compensate for any slowdown that he may physically have to get the job done.

STEPHANIE SY: Let's talk about some of the questions voters have with an expert in aging, cognition and memory.

Dr. Brad Dickerson is a neurologist at Massachusetts General Hospital and Harvard Medical School.

Dr. Dickerson, thank you so much for joining the "News Hour."

Before we even start this conversation, let's just get out of the way that neither of us wants to be making ageist generalizations here.

We all know there are 94-year-olds out there who are sharp as tacks.

Having said that, what concerns and questions have come up for you about the abilities of the two presumptive nominees for president?

DR. BRAD DICKERSON, Professor of Neurology, Harvard Medical School: Yes, Stephanie, I think you make a good point, which is that, as a neurologist, I have seen 60-year-olds that really have significant cognitive impairment, and I have seen 85-year-olds that are sharp as a tack, as you just said.

I feel like the biggest issue is that, as we all get older, it's more and more common that diseases associated with aging may start to take hold in the brain.

And they can often be very insidious as they first do that.

STEPHANIE SY: Dr. Dickerson, I want to play two clips here.

The first is President Biden from the recent debate where he seemed to lose his place during an answer about the national debt.

The second piece of sound is the former president at a rally back in January when he confused the names of former Speaker of the House Nancy Pelosi and his primary rival, Nikki Haley, when talking about security issues tied to the January 6 assault on the Capitol.

JOE BIDEN, President of the United States: We'd be able to right -- wipe out his debt.

We'd be able to help make sure that all those things we need to do, childcare, 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 have been able to do with the -- with the COVID -- excuse me -- with dealing with everything we have to do with -- look, if -- we finally beat Medicare.

JAKE TAPPER, Moderator: Thank you, President Biden.

President Trump?

DONALD TRUMP, Former President of the United States (R) and Current U.S. Presidential Candidate: Nikki Haley, you know they -- did you know they destroyed all of the information, all of the evidence, everything, deleted and destroyed all of it, all of it because of lots of things.

Like, Nikki Haley is in charge of security.

We offered her 10,000 people, soldiers, National Guards, whatever they want.

They turned it down.

They don't want to talk about that.

These are very dishonest people.

STEPHANIE SY: Dr. Dickerson, when you hear those clips, do you see two men simply battling normal aging?

And should that in itself be worrying?

Or do you see the potential presence of neurological disease such as dementia or Parkinson's, which would, of course, be worrying?

DR. BRAD DICKERSON: Yes, Stephanie, I think we all recognize that it's common as we get older for our thinking processes and our movement to slow down.

And that can be particularly evident when people are trying to speak rapidly, especially in the setting of a debate.

So I don't necessarily think we need to read too much into isolated incidents like this.

And it's also very common for fatigue or other things that make us all feel a little bit under the weather to magnify issues that people have as they're getting older.

I think the question really is, how consistent are these changes relative to each of the candidates' previous baselines?

STEPHANIE SY: And we do have some idea of their baseline because they have both held office, Trump for four years and Biden for many years before that.

I'm sure that you have seen sort of their previous performance in previous years.

So what is your assessment of whether we should be concerned?

DR. BRAD DICKERSON: Yes, I mean, I think that they have changed both of them relative to their previous baselines, as we have seen.

I think that's what's really getting everyone's attention, is, this seems a bit out of character for both of them in some ways.

And so I do think it's legitimate to be asking, should we be having cognitive assessments that we might use for any leader that's coming into a position of power or a position where they have responsibility?

Of course, in many business sectors, candidates for CEO or, of course, as we know, pilots are examined and assessed for a variety of issues before they take over those jobs.

STEPHANIE SY: Supporters of both Mr. Trump and Mr. Biden point to the accomplishments in their first terms, but the argument I have heard is, what will a President Biden be like in 2026 or a Trump in 2026?

Is there a specific cognitive test that both men could take to help elucidate that for voters?

And what clues could a cognitive test provide us?

DR. BRAD DICKERSON: Yes, so the cognitive test that people talk about a lot is the Montreal Cognitive Assessment, or the MoCA.

And there are similar tests that are 30-point cognitive screening tests that take about 10 minutes and are often performed by primary care doctors to screen for a decline in memory or language or other thinking abilities.

Healthy older adults typically score above a 26.

But it's important to keep in mind that these tests need to be considered in the context of all the other information we know about people.

They shouldn't be interpreted in isolation.

It's also common for patients who have a high level of education or occupational attainment to pass these tests, even if they may have symptoms of cognitive decline.

And, in that case, people would typically be referred for more specialized evaluations by a neurologist or a neuropsychologist.

STEPHANIE SY: When we talk about cognitive decline, I'm reminded of one of the voices we heard earlier who acknowledged Biden is slowing down.

He sympathizes, he said, with him.

But are these lapses in being able to express oneself publicly necessarily indicative of one's cognitive abilities?

DR. BRAD DICKERSON: I think speech and language is becoming very clearly a marker that we're investigating as an indicator of early cognitive impairment.

But we also recognize that we have to compare people that we might be studying for that question with what we call age-matched control, so people of similar age that don't have the neurological illness that we might be studying.

So I think we see that there are lots of variability in people's speaking abilities as they simply get older, even if we know that they do not have neurologic disease.

But we also know that speech and language changes can be early features of certain neurological diseases.

So I think it's very difficult to separate just simply on the basis of speech and language alone.

STEPHANIE SY: Dr. Brad Dickerson with Massachusetts General Hospital and Harvard, thanks so much for your expert opinion.

DR. BRAD DICKERSON: My pleasure, Stephanie.

Thank you very much for the invitation.