Americans are accustomed to knowing who won on election night because news organizations project winners based on partial counts, not because the counting is actually completed that quickly. These race calls mean Candidate A is far enough ahead that, given the number of outstanding ballots and the regions those ballots are coming from, Candidate B would realistically be unable to close the gap.

The difference this year is not the timing of final results — those will come, as always, by the certification deadlines each state has set, ranging from two days after the election in Delaware to more than a month after in California. The difference, rather, is when news organizations are likely to have enough information to make accurate projections.

If, as Mr. Trump suggested, courts were to force states to stop counting after Nov. 3, it would be an extraordinary subversion of the electoral process and would disenfranchise millions of voters who cast valid, on-time ballots.

“Everyone — including Joe Biden, the Democrat Party, the mainstream media and the American public — should want election results they can trust and for every valid ballot to count,” said Thea McDonald, a spokeswoman for Mr. Trump’s campaign. “President Trump and Republicans have long fought for these key principles of our democracy, and in many states won, in the fight against Democrats’ attempts to effectively delay Election Day.”

Ms. McDonald pointed to efforts in some states to accept ballots that are received late if they were postmarked by Election Day — or, in some cases, if the postmark is not clear — and said this was “exactly the kind of late ballot counting President Trump has been fighting to prevent.”

Still, the enthusiasm Mr. Trump stirs in his supporters remains a factor in the election. Linda Shoop, of Halifax, Pa., said she did not vote in 2016 but not for lack of a preference: A Trump supporter, Ms. Shoop has arthritis and struggles to get around. But with absentee voting more widely accessible this year, she said she would vote by mail for the president.

“He has common sense,” Ms. Shoop said, describing him as more forthright than a longtime politician like Mr. Biden. The president, she said, “doesn’t lie to you. If he says he’s going to do something, he goes and he does it.”

If the president is defeated, the most obvious explanation may be his weakness with women. Mr. Biden led Mr. Trump by double digits among female voters in each of the four states, and in some states the advantage was so significant that it offset Mr. Trump’s strength among men.

In Arizona, for example, the president had an eight-point advantage with men but Mr. Biden was the overwhelming favorite of women, winning 56 percent of them compared with Mr. Trump’s 38 percent.

The other group that is propelling Mr. Biden is college-educated white voters, a traditionally Republican bloc that has fled the Trump-era party. The former vice president is leading by double digits among white voters with college degrees in Wisconsin, Pennsylvania and Arizona and beating him, 48 percent to 45 percent, with that constituency in Florida.

In Maricopa County, Ariz., home to Phoenix and its suburbs, Mr. Biden is winning 48 percent of the vote compared with 42 percent for Mr. Trump, according to the survey. In 2016, Mr. Trump won the county by three points.

Mr. Biden is also poised to become the first Democrat in 20 years to carry older adults, the voters who are most at risk with the coronavirus. In Wisconsin and Pennsylvania, the former vice president is leading by double digits with older voters. And in Florida and Arizona, retiree havens with wealthier and more tax-phobic seniors, Mr. Trump is effectively tied with Mr. Biden among older voters despite having won with them convincingly in both states in 2016.

The president remains in contention in Florida on the strength of his support from working-class whites and his gains among Hispanic voters. He’s running more competitively with Florida Latinos than he did in 2016, and 9 percent of them remain undecided.

Hispanic men in Florida, in particular, are more willing to support Mr. Trump. The poll found the two candidates splitting this group almost evenly, with Mr. Biden ahead by just one point. But the president is facing an even larger gender gap in the Hispanic community than he is over all: Latinas favor Mr. Biden by 39 points.