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We're just more than three weeks from Election Day, and the polls are still tied. Since modern polling began, there's never been a race this close for this long. Neither candidate has been able to establish a lead outside the margin of error. And it's raised a lot of questions about what polls can and can't tell us. NPR's senior national political correspondent Mara Liasson has this report.
MARA LIASSON, BYLINE: One thing pollsters know for sure is the makeup of today's voting age population. For that, they rely on demographers like Bill Frey from the Brookings Institution. Cycle after cycle, Frey tracks the changing universe of possible voters.
BILL FREY: The big shifts really are a decline in what we call the white, non-college voters. They're now less than 40% of eligible voters. Back when Obama first got elected, they were over half of eligible voters.
LIASSON: Identifying the voting age population, in other words, eligible voters, is relatively simple. Predicting the electorate, that is who will actually vote, is much more complicated, says Lee Miringoff, who conducts the NPR/PBS News/Marist poll.
LEE MIRINGOFF: Not everybody votes, so you need to determine the likely voters. And that's not easy because just asking people whether they intend to vote or not because of civic pride and social desirability, people will tend to overestimate the likelihood that they're going to vote.
LIASSON: So every poll starts with a big guess, a theory about who will turn out. It's an educated guess says Republican pollster Nicole McCleskey, who looks to data on past voter behavior.
NICOLE MCCLESKEY: One of the best predictors of what's going to happen in the future is what has happened in the past. So yes, absolutely, you have to look to vote history because that is the most reliable indicator.
LIASSON: So if a voter has voted in the last three or four or five elections, she'll probably vote this year too. And McCleskey looks to other forms of historical data to create her turnout model.
MCCLESKEY: We know that the voting pop sample will 47% male, 53% female. It has historically been that way, and it will be in this election. So we set a quota for 47% male, 53% female.
LIASSON: Democratic strategist Tom Bonier, who runs the analytics firm TargetSmart, has been paying close attention to data about newly registered voters.
TOM BONIER: We know that there was a big real change in the electorate when Vice President Harris became the nominee, where we saw this spike of new voter registrations from younger voters, women and voters of color.
LIASSON: When someone takes the deliberate action of registering to vote, Bonier says, they're much more likely to turn out to vote. Pollsters strive to create the most accurate model of the electorate that they can. But in a deeply divided, evenly divided country, polling has its limits says Lee Miringoff.
MIRINGOFF: This is the longest time in our history where no political party has dominated. The House, Senate and the White House could all change parties. They're all that close. So the polls, in a sense, are being asked to be more precise than the instruments are.
LIASSON: One question hanging over this election is which candidate will end up overperforming their polls. Democratic strategist Simon Rosenberg points out that Trump's support was underestimated, or under polled, both times he's run for president. But since 2022, when the Supreme Court overturned Roe v. Wade, the voters polls have missed have been Democrats.
SIMON ROSENBERG: The elections since the spring of 2022 have been remarkably consistent here in the United States, where Democrats have overperformed polls and Republicans have underperformed. And the question is, is this election going to look like all those other elections going back to spring of 2022, or will - because Trump is on the ballot, right? - will it revert back to 2016 and 2020, where Trump did better than expected?
LIASSON: And that's a question only voters, not pollsters, can answer. Mara Liasson, NPR News.
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