FORT COLLINS, Colo. (AP) — Standing in a line of thousands outside an arena at Colorado State University, Aleksandr Cronk contemplated the grim possibility that the man he was waiting to see, Bernie Sanders, may not make it to the November ballot and he'd have to decide whether to vote for Hillary Clinton.

Like millions of young voters nationwide, Cronk has been electrified by Sanders' longshot bid for the Democratic presidential nomination. Even as Clinton has racked up a commanding lead in the contest, she's overwhelmingly losing voters between ages 18 and 29 in early-voting states. Her lukewarm reception among people like Cronk points to a challenge for her in November, should she win the nomination. Overwhelming support from young voters twice helped secure the White House for Barack Obama.

"I don't think there's going to be a lot of change" if Clinton wins, said Cronk, 21. Like many younger voters he's especially alarmed by income inequality, the issue that Sanders has made a centerpiece of his campaign. "The Clintons don't really stand in that position very well."

Clinton's weakness with younger voters has stood out consistently this year — she lost Democratic primary voters who are aged 18 to 29 by 70 points in Iowa, 68 points in New Hampshire and 25 points on Super Tuesday, when she won seven of the 11 states in play for Democrats.

"Hillary's weakness with millennials has to be very worrisome for the Democratic Party," said Simon Rosenberg, president of the New Democrat Network, a center-left advocacy group. "What you're seeing is the millennial generation has essentially seceded from the Democratic establishment."

Obama's presidential campaigns showed the power of voters under 30, who gave him 2-1 support in both 2008 and 2012. In 2016, even more millennials than Baby Boomers are eligible to vote, and they make up a large share of potential voters in battleground states such as Ohio, Pennsylvania and Iowa, demographers say.

For months Clinton tried to connect with younger voters through famous supporters such as singer Katy Perry and actor Lena Dunham. She embraced the anti-police-brutality movement Black Lives Matter, spearheaded by young African-Americans, and vowed to expand President Obama's deportation relief for young people in the country illegally and their families. She promised debt-free college for all, only to be one-upped by Sanders' pledge of free college for all.

Clinton has acknowledged she's fallen short, saying she has to work harder to convince young people she will help them. When an Iowa college student asked her in January why so many other youths found her dishonest, Clinton blamed decades of Republican attacks.

"I have been around a long time and people have thrown all kinds of things at me and I can't keep up with it," replied Clinton. "If you are new to politics and it's the first time you've really paid attention, you go, 'Oh my gosh, look at all of this.'"

Joelle Gamble of the Roosevelt Institute, a liberal New York think-tank, said young voters are increasingly distrustful of institutions like political parties. She noted that, on the Republican side, many have rallied around Texas Sen. Ted Cruz, who boasts of how hated he is by Washington Republicans.

"I don't think there's any one candidate that can fix this," she said.

Sanders, a socialist senator who was an independent until launching his quixotic Democratic primary run last year, has come the closest. His call for a political revolution has reached people like Daniel Harty, a 21-year-old computer science student in Las Vegas who once saw himself as a libertarian but registered as a Democrat to support Sanders. Should Clinton be the nominee, Harty said, he'd never back her. "Hillary Clinton doesn't seem like a genuine person," Harty said. "She changes her opinions based on what's politically expedient."

Jay Morris, 24, of Oklahoma City, has $72,000 in student debt and no job. A Sanders supporter, he said he'd never back Clinton. "I think she's completely entrenched in the political machine," he said. "I just wouldn't vote."

Michelle Williams, 20, a natural resources student, didn't pay attention to politics until the hashtag #FeeltheBern began popping up in her social media feeds. She was excited to see Sanders speak in Fort Collins. "He keeps it real about how America truly is," she said. But she would drop out of politics if the nominee were Clinton. "She's weird," Williams said.

Cronk has a running debate with his parents about his support of Sanders. They're Clinton voters, fearful of what Republicans could do to Sanders in a general election. Cronk, on the other hand, was in elementary school when a Republican last won a presidential election and believes the increasing divide between the wealthy and everyone else demands dramatic action.

He worries whether he'll be able to have the same life as his parents, a librarian and part-time teacher who own a house in a nice San Diego, California, neighborhood. "To see how quickly the gap is increasing is kind of scary," he said.

Cronk said that, if it came down to it, he'd vote for Clinton in a general election. She'd be better than whoever emerges from the Republican primary, he said. "You feel kind of forced."