Neither Joseph Mitchum nor Laura Brooks participated in the last presidential election four years ago.

But they and voters like them could very well decide the outcome of this November’s race for the White House.

Mitchum, who hails from battleground Georgia, and Brooks, who lives in Michigan, both participated in NBC News surveys this year and told pollsters that they’d support former President Donald Trump over President Joe Biden — reflecting a broad trend across public polling showing Trump with a sizable advantage among those who didn’t vote in 2020.

Findings from NBC News’ last three national polls — all taken before last week’s debate — show a whopping 25-point swing toward Trump among voters who didn’t participate in both 2020 and 2022, compared to voters who cast ballots in the last two national elections.

If those voters turn out this time, it could make the difference between winning and losing for Trump. And both Mitchum and Brooks underscore the big question of whether these non-2020 voters will actually show up in November.

Mitchum, 24, said he’s definitely voting in 2024 — after not being registered to vote in 2020. “Yes, I am going to vote,” he told NBC News in a follow-up interview.

“I really don’t like what’s going on with our border,” he added, explaining why he supports Trump. “Another is I am partial to my gun rights.”

But Brooks, 25, said in her follow-up interview that she’s probably not voting in November, though she said she’d support Trump in a poll. (Like Mitchum, Brooks wasn’t registered to vote in 2020.)

“Biden, he seems to be just a little senile now,” she told NBC News. “And with Trump, there’s all the legal stuff around him that’s happening.”

“I’ve never seen such a pony show,” Brooks added.

Biden’s frequent voters versus Trump’s infrequent ones

In 2020’s presidential election, a record 159 million Americans turned out to vote. Still, tens of millions of eligible people like Mitchum and Brooks didn’t participate, representing a significant segment of the potential electorate that could tip 2024’s outcome.

NBC News’ polls in November 2023, January 2024 and April 2024 interviewed a combined total of 3,000 registered voters, most of whom were matched to historical voter files across the states.

Of those who participated in both the 2020 presidential election and 2022 midterms — representing 56% of all interviewed voters — Biden led Trump by 5 percentage points, 49% to 44%, according to the merged polling.

But among those who voted only in 2020 — representing 17% of the interviews — Trump was ahead by 12 points, 50% to 38%.

And Trump’s lead over Biden was even bigger among those who didn’t vote in 2020 (by 16 points) and those who didn’t vote in both 2020 and 2022 (by 20 points).

Looking at it this way, this election could come down to Biden’s frequent voters versus Trump’s infrequent ones.

“Trump’s positive margins over Biden are coming from more infrequent voters — people who voted in 2020 and skipped the midterm election in 2022, or who have not voted in either election,” said Republican pollster Bill McInturff, who co-conducts the NBC News poll.

It’s not just the NBC News national poll that finds Trump overperforming with infrequent voters; surveys from The New York Times and the Cook Political Report with Amy Walter also show it.

Will the infrequent voters show up in November?

The challenge for Trump, however, is that these non-2020 voters show far less interest in the upcoming presidential election — and thus are potentially less inclined to actually vote in November.

The same merged NBC News polling finds 73% of voters who participated in the 2020 and 2022 rated themselves as having high interest in the upcoming presidential election, giving themselves a “9” or “10” when asked to rate their interest on a 10-point scale. Only 44% of those who didn’t vote in 2020, and 37% who voted in neither 2020 nor 2022, rated their interest in 2024 as that high.

These findings represent an enormous shift in American politics, given that Republicans used to produce the most reliable voters, while Democrats were more sporadic.

“Forty years ago in a special election, the joke was ‘pray for rain,’ as the most dependable voters were college-educated, affluent Republicans who always voted,” said McInturff, the GOP pollster.

But today, he added, “the data is clear that the consistent voter tips towards Biden.”

Who are the voters who didn’t participate in 2020?

According to NBC News’ polling, the non-2020 voters disproportionately describe themselves as political moderates. They tend to lack college degrees. And they are more likely to be younger voters.

But some of them are older, like Maria Calderon, 52, of Houston. She explained why she didn’t participate in the 2020 election: “I had a lot going on in my life at the time.”

Yet she told NBC News she will vote in November. “I’m gonna vote this year,” she said. “It would be for Donald Trump, 100%.”

The infrequent voters also have much more negative opinions of Biden than they do of Trump.

According to NBC News’ combined polling, Biden’s net favorability rating sinks from minus-9 among 2020 and 2022 voters to minus-31 among those who didn’t vote in either of the past two national elections. Trump’s trend is the reverse, from minus-6 among those who didn’t vote in 2020 and 2022, to minus-21 among those who participated in both.

“I’m not voting,” said Vivian Lambert of Augusta, Georgia, who didn’t participate in 2020. “But it would be Trump.”

“I just hear so many bad things about Biden,” Lambert continued.

Still, not all of these infrequent voters are Trump backers. Kelly Torz of Michigan, 25, says she didn’t vote in 2020 but will vote for Biden in November, because of her support for abortion rights, the environment and LGBTQ issues.

“I care a lot about the environment, and Biden is going to hopefully help keep the ecosystem in a better condition than I believe Trump would,” Torz said.

And again, it’s not a certainty that all of these voters who didn’t participate last time will participate in 2024.

“Most likely I am,” said Noah Fimon, 19, of Louisiana, who supports Trump.

This article was originally published on NBCNews.com