It’s usually difficult to get a clear look at which way the youngest voters are leaning. Pollsters have trouble reaching them, and they’re often excluded when a survey breaks out its results by group. But they make up a significant portion of the vote. In 2012, voters younger than 25 accounted for about 9 percent of the electorate, a slightly larger share than Latinos did. That same year, according to the American National Election Studies, they favored President Obama by 29 percentage points over Mitt Romney.

Without good data, you might assume that Hillary Clinton is doing just as well with this group. She is essentially running for a third Obama term, after all. But new SurveyMonkey data (shared with FiveThirtyEight) suggests that Clinton is winning under-25 voters by half as much as Obama did. And, moreover, the data suggests that these voters should be solidly Democratic.

Unlike many other pollsters, SurveyMonkey interviews thousands and thousands of people each week, so they’re able to get a good sample of young voters. From Aug. 22 to 28, SurveyMonkey interviewed about 1,200 registered voters ages 18 to 24. Among them, Clinton led Donald Trump 41 percent to 27 percent, with 17 percent for Libertarian Gary Johnson and 10 percent for the Green Party’s Jill Stein.

What makes Clinton’s standing with those under 25 especially interesting is that older millennials are more likely to back her. Among voters ages 25 to 35, Clinton is leading 46 percent to 24 percent over Trump, with Johnson at 18 percent and Stein at 7 percent.

Are younger millennials simply more Republican-leaning? It doesn’t seem so. In fact, under-25 voters are more likely than any other age group to approve of the job Obama is doing as president. Here’s Clinton’s lead over Trump and Obama’s net approval rating by generation (18-24 are young millennials, 25-35 are older millennials, 36-51 are Generation X, 52-70 are baby boomers, and those older than 70 are members of the silent generation or the greatest generation).

VOTER AGE CLINTON’S MARGIN OVER TRUMP OBAMA’S NET APPROVAL RATING DIFFERENCE 18-24 +13 +32 -18 25-35 +22 +23 -1 36-51 +2 +2 +0 52-70 -3 -7 +3 71+ -7 -13 +6 Clinton is underperforming among the youngest voters Data is rounded Source: Surveymonkey

Generations that like Obama are voting for Clinton, and generations that don’t like Obama are voting for Trump. The only real exception is the under-25 group. (If Clinton’s numbers among younger millennials matched their approval of Obama, her overall lead would be about 2 percentage points larger.)

Under-25 voters aren’t backing Trump in unusually large numbers. Instead, they’re either backing a third-party candidate or saying they’re undecided. (Bernie Sanders did especially well with those under-25 voters in the Democratic primary.) Indeed, when SurveyMonkey asks 18- to 24-year-old voters to choose between Clinton and Trump (i.e., no Johnson or Stein), Clinton’s lead expands from 13 percentage points to 23. That’s the biggest jump for Clinton among age groups between the four-way and two-way race.

CLINTON’S MARGIN OVER TRUMP VOTER AGE FOUR-WAY CONTEST TWO-WAY CONTEST DIFFERENCE 18-24 +13 +23 +9 25-35 +22 +26 +4 36-51 +2 +3 +1 52-70 -3 -3 +1 71+ -7 -8 +0 Young voters are more likely to pick Clinton without third-party candidates Data is rounded Source: Surveymonkey

If the race continues to tighten, some voters younger than 25 might go back to their Democratic roots. Right now, they might feel like they can cast a protest vote for a third-party candidate without contributing to a Trump victory. That would be good news for Clinton. The bad news for Clinton is that we’re less than two months from Election Day, and there’s no sign that the third-party candidates’ share of the vote is fading. If Clinton is trying to reassemble Obama’s winning coalition, the youngest voters are proving to be her weakest spot.