AMNA NAWAZ: Primary voters in Maine, Nevada, North Dakota, and South Carolina will set their party's respective lineups for November's general election tonight.

But in one of those states, voters may also amend their Constitution to keep certain candidates off the ballot and out of Washington.

Lisa Desjardins explains.

LISA DESJARDINS: Across North Dakota's wide landscape, an unusual test of democracy's boundaries, on Tuesday's primary ballot, a potential age limit for the state's members of Congress.

JARED HENDRIX, Chairman, Retire Congress North Dakota: On every campaign, you're going to have, obviously, direct-mail postcards.

LISA DESJARDINS: Political consultant Jared Hendrix is leading the effort.

JARED HENDRIX: We do think that there is a lot of wisdom that comes with age.

But, of course, there's a limit, to where we all face a decline of some kind at some point.

And so we wanted to try to find the right balance.

We thought 80 was the balance.

LISA DESJARDINS: The result is Measure 1, an amendment to the state constitution which says members of Congress cannot be over 80 before the end of their term, meaning, to run for a full term.

A U.S. Senate candidate can be no more than 75 and a House candidate no more than 79.

To get it on the ballot, Hendrix, who is also running as a Republican for the state legislature, and others gathered and submitted more than 40,000 signatures.

How did you choose the age?

JARED HENDRIX: The reason we picked the age of 80 was simply that the support is so overwhelming at that point.

Some of the first people I talked to when I decided to take it on are my parents.

They're in their early 80s.

And I asked my dad: "How do you feel about this?

Am I crazy?"

And he said: "Son, at my age, I have got no business being in Congress."

LISA DESJARDINS: National polls show broad concern about age.

In a recent Pew Research Center survey, a whopping 79 percent overall, with little partisan divide, backed age limits for federal office.

One factor may be the presidential candidates.

In a February ABC News/Ipsos poll, nearly 60 percent said that both President Biden, age 81, and former President Trump, who turns 78 this week, are too old for another term as president.

Measure 1 in North Dakota does not apply to presidential candidates.

Hendrix says that was a practical legal choice.

But the candidates themselves have acknowledged age concerns.

QUESTION: Something the special counsel said in his description, you are a well-meaning elderly man with a poor memory.

JOE BIDEN, President of the United States: I'm a well-meaning, I'm an elderly man, and I know what the hell I'm doing.

DONALD TRUMP, Former President of the United States (R) and Current U.S. Presidential Candidate: I said to the doctor, who was Dr. Ronny Jackson, I said, is there some kind of a test, an acuity test?

And he said, there actually is.

And I got a perfect mark.

FMR.

SEN. STROM THURMOND (R-SC): There is nothing which compares to serving here.

LISA DESJARDINS: Aging in Congress is nothing new.

Former South Carolina Senator Strom Thurmond served beyond his 100th birthday.

But the U.S. Senate in particular is getting older as a group.

Current Iowa Senator Chuck Grassley is 90 years old, and 21 senators and representatives are in their 80s.

North Dakota's congressional delegation is relatively young in comparison, 67, 63 and 47.

JARED HENDRIX: We didn't want it to be targeting our current members.

It wasn't about any individual.

It's about the principle of the issue.

When people say that it's not a problem here, my response is, well, it's not a problem here yet.

DAVE PETERSEN, North Dakota Voter: I did vote against it.

JO PETERSEN, North Dakota Voter: And I voted for it.

LISA DESJARDINS: In Grafton, North Dakota, Dave and Joe Petersen are in their 70s.

They're very active.

She chairs the local hospital board, and he's running for a municipal judge.

DAVE PETERSEN: It's probably not as rigorous, for example, as being in Congress or anything like that.

But, yes, I'm older than I was five years ago.

LISA DESJARDINS: They agree on an urgent need for younger candidates, but Dave thinks voters, not a law, should decide about age.

DAVE PETERSEN: I don't think you can automatically say someone because of their age is unable.

It's true, but I think the voters need to decide that.

LISA DESJARDINS: Joe says the current presidential race convinces her otherwise.

JO PETERSEN: I don't know if it should go as far as the voter.

It's a frightening thing to me.

When I look at our two presidential candidates, I'm not sure in my heart if I could vote for either one of them.

And a lot of it has to do with age.

LISA DESJARDINS: While the Petersens are split, Tina Matz and Elizabeth Kensinger, experts with Boston College's Research on Aging Group, are on the same page.

CHRISTINA MATZ, Boston College: Overall, chronological age is not a good proxy for almost anything.

ELIZABETH KENSINGER, Boston College: There's just a fascinating ebb and flow of what we're best at different points in our life, such that a 40-year-old is going to have a different set of strengths and weaknesses than a 60-year-old, than an 80-year-old.

LISA DESJARDINS: Their research suggests older workers can draw on a deeper knowledge base and are generally more emotionally regulated than their younger peers.

Precision memory and processing do slip with advancing age, but Matz and Kensinger argue, symptoms should concern voters, not years.

CHRISTINA MATZ: Age is one of those last isms that still tends to be socially accepted.

And I think we stereotype ourselves in terms of age.

We make jokes about people's age.

And there's not a whole lot of credibility behind it.

LISA DESJARDINS: There is also, of course, a legal question.

Nearly three decades ago, the Supreme Court struck down term limits for federal lawmakers in 23 states.

In its 5-4 decision, the court determined that states could not impose stricter qualifications than the U.S. Constitution.

Legal experts we spoke with about the North Dakota case are skeptical of its courtroom chances.

JARED HENDRIX: Certainly not naive.

I mean, I suspect it would be challenged legally.

But I think it's a great question to ask.

Do we have a right as states to apply additional qualifications?

And we hope the courts would rule that way, but we will see what they do.

LISA DESJARDINS: Whether this survives a court challenge or not, the idea of an age limit for elected officials is broadly popular and bipartisan and increasingly a topic of conversation, not just in North Dakota.

For the "PBS NewsHour," I'm Lisa Desjardins.