President Barack Obama speaks at a campaign event at Cornell College, Wednesday, October 17, 2012, in Mt. Vernon, Iowa. (AP Photo/Carolyn Kaster)   Gustavo Delgado, 22, will be in Nevada this weekend, campaigning for President Obama. When I first spoke with him in mid-September, he was working full-time in Los Angeles, far from the mayhem of the horse race and unsure whether he’d be involved in the presidential campaign, despite having committed more than a year to Obama for America in 2008.

Since then he’s become alarmed by how close the race really is. “We could lose this election,” he told me earlier this week, “and everything we’ve done for the past five years could slip away.” He said he wishes now he’d been able to devote more of his time, but that by going to Nevada he’ll be “making a small sacrifice and playing whatever part I can play.” 

Given the razor-thin margin between Barack Obama and Mitt Romney in swing states like Nevada, such sacrifices from young voters are far from small. The race will hinge on turnout, and millennials—some 64 million eligible voters—have emerged as the main question mark among the constituencies the candidates have been courting.

Romney won’t win the youth vote: the fall survey from the Harvard Institute of Politics, which polls young Americans twice yearly, shows Obama leading Romney by a nineteen-point margin among millennials who say they are likely to vote and by twenty-two points among young adults in general. For most millennials the choice is between voting for Obama and not voting at all.

Historically, young voters engage late in electoral politics, and data released by the Center for Information and Research on Civic Learning (CIRCLE) just last week show that millennials’ intention to vote, along with political engagement and support for Obama, has risen steadily since the summer.

But the number of millennials who say they will vote remains lower than in past years—fewer than half in the Harvard poll. That may reflect general disinterest in electoral politics, but it also mirrors a corresponding drop in the number who are registered to vote in the first place. The percentage of young Americans who are registered this year is the lowest of the past five presidential elections. Only half of adults under 30 say they are sure they are registered, down eleven points from 2008 and seven points from 2004. Several factors account for the decline, including shrinking infrastructure for nonpartisan youth engagement and the lack of Democratic primaries, leading to an organizing effort focused on a handful of states.

Even among registered voters under 30, however, the expected turnout is nine points lower than it was at the same time in 2008. The fissure between first-time voters, who appear to be more conservative than their older peers, may also lessen the impact of millennial voters. And while Romney supporters account for a smaller portion of millennials, they appear likely to turnout in higher percentages than young Obama supporters.

Perhaps the most critical and unpredictable segment of the millennial electorate is young Latinos. Staunch Obama supporters when they vote, young Latinos are the group that appears least likely to do so. Maria Teresa Kumar, the president of the youth civic engagement group Voto Latino, says that Latino millennials, most of whom are English speakers, fall into a hole between two groups targeted by the campaigns: their Spanish-speaking parents and their non-Hispanic peers. “This is a group of Americans that doesn’t have appropriate political media to consume,” Kumar says. “They’re so new to the political process, and they just haven’t been targeted.”

Swing states in the South and West—notably, Florida, Colorado and Nevada—have high concentrations of young Latinos, but Kumar says that the group also stands to impact races in swing states where they aren’t considered a key constituency, like Ohio, where Latino populations have surged in cities like Dayton and Toledo. “If Ohio, Virginia, North Carolina and Pennsylvania decide the race, it will be in large part because of a group that no one is paying attention to,” she says. The most important factors on Tuesday will be the strength of get-out-the-vote efforts led by community leaders, particularly Latino celebrities and radio DJs, as well as the legacy of voter ID. “A lot of misinformation is spreading that disproportionately targets Latinos,” Kumar says, mentioning billboards she’s seen in Pennsylvania that still say “Don’t forget your ID” in Spanish, even though that state’s law is no longer in effect. “It’s confusing, and it is going to have an impact, not just in this election but in elections to come.”

In fact, data from CIRCLE shows that most millennials do not know three essential facts about voting: the deadline for registration, whether they have the option to vote early, and whether they need a particular form of government ID to vote. Lizzy Stephan, an organizer in Colorado and one of the millennials I interviewed in September, said last week that the election buzz among young people in the state has built dramatically since the debates. But, she wrote in an email, “I’m also seeing a lot more frustration as the actual voting happens about how difficult it is to navigate the whole process.”

On Tuesday, then, look for the millennial vote to be a referendum not just on the presidential candidates, but on the American system of politics in general. For more on millennials and election 2012, check out my article from the November 5 issue of The Nation.