Young Voters Helped Democrats. But Experts Differ on Just How Much.

Mr. Bonier, from the Democratic data firm TargetSmart, was among the first to take note of an upward curve in early voting by young people. In an interview, he said he disagreed with Mr. Shor’s analysis, but that it was far too early to make sweeping statements about what happened.

“We did see, in the last week of early voting, that the youth vote really began to surge,” he said, “which would suggest that the notion that the youth vote would come out on Election Day was valid.” But only an analysis of all the votes will determine whether that was true.

There is another theory, though, hinted at in some of the numbers. It argues that voting by young people was down overall from 2018 — but higher in the states where it counted.

Analysts at Circle, for example, concluded that while 27 percent of young voters turned out nationwide, that number rose to 31 percent in nine key states. Republicans did well in three — Florida, North Carolina and Ohio — but the remaining six were all states where Democrats scored notable victories, such as Michigan New Hampshire, Pennsylvania and Wisconsin.

Mr. Shi, of Voters of Tomorrow, made the same point. “If you look at the battleground states, what we see is young Democrats surging and young Republicans staying home.” He said he believed that the extremist positions of Republican candidates in those states riled up young Democrats but had the opposite effect on Republicans.

In Wisconsin, the director of the state Democratic Party, Ben Wikler, offered his own statistic: Just before the 2018 midterms, the state claimed 654,000 registered voters under age 35. This year, he said, the comparable figure was 783,000 — a 20 percent increase.

He said that rules allowing new voters to register on the same day they cast ballots drove some of the rise, as did an intensive effort to recruit young voters that the state Democratic Party launched in 2019.