Hillary Clinton's campaign has gone back to college, dispatching the nominee and popular Democrats to campuses in battleground states to issue a blunt warning: Blow off voting Nov. 8 - or back a third-party candidate - and you help elect Donald Trump.

Polls show weak support for Clinton among the young voters who were a key piece of the winning coalition President Obama assembled in two elections. They don't like Trump necessarily, but many are not enthusiastic about the former secretary of state.

So last week, Vice President Biden visited Drexel University, and first lady Michelle Obama held a rally at La Salle, while Clinton campaigned at the University of New Hampshire with vanquished primary foe Vermont Sen. Bernie Sanders, who electrified millennial voters. Clinton had appealed to Temple University students on Sept. 19.

Taking selfies at rallies is fun, Michelle Obama said Wednesday at La Salle, but this election is serious business.

"Here's the truth: Either Hillary Clinton or her opponent will be elected president this year. And if you vote for someone other than Hillary, or if you don't vote at all, then you are helping to elect Hillary's opponent," the first lady said. "And the stakes are far too high to take that chance. Too high."

Recent polls also show Clinton winning under half the votes of millennials, defined generally as people between ages 18 and 35. Obama got more than three-fifths of this demographic in both of his campaigns.

Clinton is losing younger voters to Libertarian Gary Johnson and Green Party candidate Jill Stein, analysts say. She does better when pollsters present a binary choice between Clinton and Trump.

In a Sept. 19 Wall Street Journal/NBC News poll, Clinton led Trump 50 percent to 34 percent among millennials. With the minor-party candidates included, Clinton had 38 percent, to 26 percent for Trump, 17 percent for Johnson, and 5 percent for Stein. Those percentages for Johnson and Stein were almost double what they drew among all voters.

Clinton needs to knock down the third-party vote - and fast, Democratic strategists argue.

"They've got to peel them off," David Plouffe, Obama's 2008 campaign manager, told Bloomberg TV. "It's the most important thing left in the campaign."

At La Salle, where students danced to Taylor Swift before Michelle Obama arrived, the first lady's argument that a Trump presidency is too dangerous to be contemplated resonated with Ian Frasca, 18, of Fox Chase.

He plans to vote for Clinton "because Trump's the other option," he said. "That's pretty much it." Frasca, a La Salle student, supported Sanders in the primary.

Taylor Costello, 20, and Zachary Van Sant, 19, who waited in line to hear the first lady outside La Salle's Tom Gola Arena, are also former Sanders supporters now backing Clinton.

"I find Donald Trump's policies to be vile and disgusting," said Costello, of Eagleville, a student at Arcadia University. "I feel more safe with Clinton than I do with Donald Trump."

Van Sant, a Montgomery County Community College student from Norristown and Sanders fan, said there was a "bit of a delay" in his decision to support Clinton after the primary, but he decided the Democratic nominee would "build on what Obama has done" and noted she has embraced more progressive ideas after the primary battle.

Millennials tend to agree with Clinton's positions on the issues - racial justice, LGBT equality, and climate change - and they like her policy proposals such as tuition-free college at state schools for students from families making less than $125,000 a year, polls find. They are less sure of her on a personal level.

Only a third of voters under 30 approve of Clinton, according to a Gallup poll earlier this month. Seventy-seven percent of voters 18 to 34 don't think Clinton is honest, the highest of any age group, according to a Sept. 14 Quinnipiac University poll.

In 2008, older millennials felt the "efficacy" of being able to elect the nation's first black president, said Kei Kawashima-Ginsberg, director of the Center for Information and Research on Civic Learning & Engagement at Tufts University, which studies the political engagement of young Americans.

"That sentiment really faded after that election," Kawashima-Ginsberg said, noting more recent surveys show "young people saying things like voting is not an effective way" to bring about social change.

Young voters were drawn to Sanders because he spoke of "our revolution," including them in an effort to change the political system itself.

"The Clinton campaign may have in some ways misunderstood young people as a shoo-in vote for a Democratic candidate," she said. Clinton "feels like a representation of the big corporations to many of them."

From the beginning, when it decided to locate its headquarters in Brooklyn, the Clinton campaign has wooed millennials. Lena Dunham and Katy Perry have been prominent surrogates, and Rachel Platten's "Fight Song" is the campaign anthem. It uses Snapchat, sprinkles around emojis, and sells ironic T-shirts.

"They're not brand loyal to either party - they're loyal to ideology and disruption of the status quo," said Jill Hanauer, a Denver-based Democratic strategist whose firm, Project New America, has polled millennials extensively.

In a rare moment during the Sept. 19 speech at Temple, Clinton acknowledged she has a lot of work to do: "I also know that even if you're totally opposed to Donald Trump, you may still have some questions about me. I get that. And I want to do my best to answer those questions."

Some may be beyond her reach.

Daniel Hall, a 21-year-old La Salle student, isn't sure who will get his vote. "My grandma, my dog, or Gary Johnson," he said.

Hall doesn't like Trump or Clinton because "I just don't like dishonest people." He reads fact-checking websites, and "from what I've seen, Gary Johnson's been the most honest one."

Hall's brother, Ian, 20, also a La Salle student, said he, too, planned to consider a third-party candidate. Ian, who describes himself as "pro-life," doesn't like that Clinton approves of abortion rights; as for Trump, "he's a very polarizing figure. He lies, it seems, almost as much as Hillary does."

Neither of the brothers, who are from Missouri, thought a vote for a third-party candidate would be wasted.

"We've had two parties for the last 100 years," said Daniel Hall. "Over time, people will be like, we don't want to have [just] two options."