Can Democrats come together by Election Day?

The party's voters are splintered across generational, racial and ideological lines, prompting some liberals to express reluctance about rallying behind a moderate presidential nominee, and those closer to the political middle to voice unease with a progressive standard-bearer.

The lack of a united front has many party leaders anxious — and for good reason. In more than 50 interviews across three early-voting states — Iowa, New Hampshire and South Carolina — a number of Democratic primary voters expressed grave reservations about the field of candidates, and in some cases a clear reluctance to vote for a nominee who is too liberal or too centrist for their tastes.

As she walked out of an event for former Vice President Joe Biden in Fort Dodge last week, Barbara Birkett said she was leaning toward caucusing for Sen. Amy Klobuchar of Minnesota and dismissed the notion of even considering the two progressives in the race, Sens. Bernie Sanders of Vermont and Elizabeth Warren of Massachusetts.

"No, I'm more of a Republican and that's just a little bit too far to the left for me," said Birkett, a retiree. She said that she'd like to support a Democrat this November because of her disdain for President Donald Trump but that Sanders would "be a hard one."

Elsewhere on the increasingly broad Democratic spectrum, Pete Doyle, who attended a Sanders rally in Manchester, N.H., last month, had a ready answer when asked about voting for Biden: "Never in a million years." He said that if Biden won the nomination, he would either vote for a third-party nominee or sit out the general election.

The lack of consensus among Democratic voters has led some party leaders to make unusually fervent and early pleas for unity.

"We get down to November, there's only going to be one nominee," Rep. James Clyburn of South Carolina, the third-ranking House Democrat, said Monday. "Nobody can afford to get so angry because your first choice did not win. If you stay home in November, you are going to get Trump back."

Vivid as the surface differences are between Sanders and Biden, what's even more revealing are the views that emerge in polling and conversations with their supporters.

A new CNN survey showed that about as many Democrats under 50 would be upset or dissatisfied with Biden as the nominee as they would be enthusiastic. And among those older than 65, views were even starker about Sanders: Just 23% said they'd be enthusiastic about him while 33% said they'd be upset or dissatisfied.

Interviews with Sanders supporters revealed a group of progressive activists who were as dedicated to him as they were in 2016 — and who were uneasy about his rivals, especially Biden. That was borne out in a new poll of New Hampshire primary voters from Suffolk University, which indicated that nearly a quarter of the Vermont senator's supporters would not commit to backing the party's nominee if it was not Sanders.

That number could drop by November if Sanders does not win the nomination: Research shows that most of Sanders' supporters eventually rallied to Clinton against Trump. Yet it would not necessarily happen easily.

Many Sanders supporters who said they would grudgingly support one of his rivals against Trump quickly added that that's all they'd do, ruling out doing the volunteer work that is the lifeblood of all campaigns.

If it all seems messy, and the party hopelessly fragmented, that's for good reason, said Kathleen Sebelius, the former Kansas governor and Health and Human Services secretary who grew up in Democratic politics as the daughter of a former Ohio governor.

"This primary is a reflection of the politics of the country at large," Sebelius said. "There are clearly differences among people who still feel incremental change is the best way of getting things done and folks who say we need more to pursue more radical change."

She said she'd be more worried if Democrats didn't have Trump as "a rallying cry," but conceded there was no candidate on the horizon who could fully unify the party's factions.