An exit-poll data point that will surely haunt Mitt Romney and his party in weeks to come: If he had been able to draw half of voters under 30 in Florida, Ohio, Pennsylvania, and Virginia, he would have won those states and the presidency.

The millennial generation — voters ages 18 to 29 — was widely expected to stay home on Election Day, deflated by partisan politics and disappointed by the president they overwhelmingly endorsed four years ago.

Instead, young voters matched their participation rate from 2008, with about 50 percent of eligible voters under 30 casting ballots. More importantly, they actually increased their share of the electorate, from 18 percent in 2008 to 19 percent this year, surpassing the proportion of voters over the age of 65 (17 percent, according to CNN exit polls).

And while President Obama's support with this subset dropped from 66 percent to 60 percent, youth voters were a key part of the coalition that lifted him to a second term.

“We’re treating this as a beginning, a new normal of what our country looks like, what our electorate looks like, and a new expectation for participation for young people,” said Heather Smith, president of the nonpartisan youth-advocacy group Rock the Vote in the aftermath. “This voting bloc can no longer be an afterthought for any party or campaign.”

For months, the conventional wisdom was that young voters were turning away from the president, no longer inspired by the historic nature of his candidacy or his promises to remake Washington. They also seemed to be turned off by the nasty tenor of both presidential campaigns.

Moreover, young voters have been slow to feel the effects of the recovery. Unemployment for the under 30s is mired at 12 percent — a fact that the Romney campaign attempted to capitalize on.

Yet Obama racked up huge margins in this age group in key battlegrounds, including leads of 25 points to 34 points in the states cited above.

Unlike other groups, young voters gave Obama an edge on handling the economy. Beyond that, their attitudes on social issues align much more closely with those of Obama and Democrats. For instance, a poll commissioned by the Harvard Institute of Politics showed that young voters preferred Obama over Romney on immigration reform (50 percent to 30 percent), health care policy (54 percent to 35 percent), and issues important to women (58 percent to 27 percent). A 2011 Pew Research Center poll last year found that 59 percent of Americans aged 18 to 30 support legalizing gay marriage.

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Some of Obama's campaign-year moves — announcing he now backs same-sex marriage, offering some young undocumented immigrants a way to stay in the country legally for two years — emphasized those issues and contributed to young voters' unexpected participation level.

“I thought the turnout would be low because I didn’t think the campaigns and the political system were treating young people particularly well. There wasn’t a particularly coherent debate going on about policy, and honestly, there was a lot of mudslinging,” said Peter Levine, director of the Center for Information and Research on Civic Learning and Engagement. “So then you have to go to the explanation that this is coming from them … that they were not enthusiastic or happy about the campaign, but they were persistent.”

It’s possible to envision national campaigns of the future making as many overtures to young voters as the Obama and Romney campaigns did to women voters this year, if they’re playing close attention to the data. Young people are not only helping to swing elections, they are changing policy.

As Matt Segal, president of the youth-advocacy group Our Time, pointed out, it's no coincidence that when youth turnout was high, ballot initiatives to validate same-sex marriage passed in four states.

There was an age when political consultants deleted young voters from their rolls, convinced they weren’t worth the effort, said Levine. Not so anymore.