“I think we are heading for a record presidential turnout at least in the modern era, and by that I mean since the franchise went to 18-year-olds,” in 1972, says Glen Bolger, a partner at Public Opinion Strategies. “And I mean not only in total numbers [but also] in terms of the percentage of eligible voters [who turn out]. The emotion behind politics … is sky-high, and I don’t think it’s just on one side. I think it’s on both sides.”

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McDonald thinks the turnout surge in 2020 could shatter even older records, estimating that as many as two-thirds of eligible voters may vote next year. If that happens, it would represent the highest presidential-year turnout since 1908, when 65.7 percent of eligible Americans cast a ballot, according to McDonald’s figures. Since 18-year-olds were granted the vote, the highest showing was the 61.6 percent of eligible voters who showed up in 2008, leading to Barack Obama’s victory. And since World War II, the highest turnout level came in 1960, with John F. Kennedy’s win, when 63.8 percent of voters participated.

Experts on both sides point to an array of indicators that signal turnout may reach new heights next year. Signs of political interest, from the number of small-donor contributions made to presidential candidates to the viewership for cable news, are all spiking. In polls, very high shares of Americans already say they are paying a lot of attention to the 2020 presidential race.

But the clearest sign that high turnout may be approaching in 2020 is that it already arrived in 2018. In last year’s midterm, nearly 120 million people voted, about 35 million more than in the previous midterm, in 2014, with 51 percent of eligible voters participating—a huge increase over the previous three midterms. The 2018 level represented the largest share of eligible voters to turn out in a midterm year since 1914, according to McDonald’s figures. Catalist estimated that about 14 million new voters who had not participated in 2016 turned out two years later, and they preferred Democrats by a roughly 20-percentage-point margin.

Yet one of the key questions for 2020 is whether Democrats will benefit as much from the likely expansion of the electorate. With Trump on the ballot directly, Republicans hope that 2020 will produce a surge not only in the younger and nonwhite voters who increased their participation in 2018, but also the non-college-educated whites at the foundation of the president’s support, who lagged last year.

The nature of the population eligible to vote is evolving in a way that should indeed help Democrats. McDonald estimates that the number of eligible voters increases by about 5 million each year, or about 20 million from one presidential election to the next. That increase predominantly flows from two sources: young people who turn 18 and immigrants who become citizens. Since people of color are now approaching a majority of the under-18 population—and also constitute most immigrants—McDonald and other experts believe it’s likely that minorities represent a majority of the people who have become eligible to vote since 2016.