In 2007, presidential candidate Barack Obama chats with Stacey Snyder, 21, in Ames, Iowa. A new coalition of voters — young and unmarried people, first-time caucus-goers, independents — carried Obama to victory. This year, that Obama coalition remains undecided. (Linda Davidson/The Washington Post)

Eight years ago, liberal Democrat Keri Neblett didn’t have much trouble deciding whom to back in the Iowa caucus. Barack Obama “captivated” her and, for reasons she couldn’t quite put her finger on, she never felt as if she could trust Hillary Clinton.

This time around Neblett, 45, is far more conflicted. She’s still having trust issues with Clinton, but she’s not entirely sold on this year’s liberal option: Bernie Sanders. Two weeks before the caucuses, she’s leaning Clinton. Maybe.

“Bernie has a very left-liberal perspective that I really believe in, and Hillary is a bit more conservative,” Neblett said. But as a crisis counselor, she finds Clinton’s views on gun control more appealing. “Two weeks from now, I don’t know if I’ll feel the same way.”

The strongest feeling Neblett has is ambivalence. “I’ve been feeling kind of lax about it this time around, almost apathetic for some reason. I don’t know why.”

In 2008, galvanized by a chance to make history, and persuaded that a new course for the country was possible, a new coalition of voters — young and unmarried people, first-time ­caucus-goers, independents — unexpectedly swelled Iowa’s Democratic electorate and pushed Obama to victory.

This year, many who made up the vaunted Obama coalition, a key target for both Clinton and Sanders, remain undecided as they struggle to get fully comfortable with backing either candidate.

Among Obama’s 2008 caucus-goers, support for Clinton is tenuous, hinging less on their conviction for her than their uncertainty about Sanders. Many of these voters are convinced that Clinton is more electable — and also the better prepared candidate for the presidency, even though they view themselves as more ideologically aligned with Sanders on most issues.

And the uncertainty appears to be growing as the caucuses approach. The latest Des Moines Register/Bloomberg Politics poll found that the number of undecided Democrats is on the rise in Iowa. Clinton’s lead over Sanders, 42 percent to 40 percent, has fallen by seven points since the last poll. It all adds up to still more opportunity for Sanders to expand his support — and a challenge for Clinton to protect hers — in the final weeks before Feb. 1.

That dynamic and the tightening race could bring more intensity to Sunday’s Democratic debate, the candidates’ fourth.

Anna Harris, 25 a recent transplant to Iowa City, was a staunch Obama supporter in her first election in 2008. Harris has settled on Clinton — but her passion lies with Sanders.

“I’m really supportive of Bernie’s ideas,” Harris said. “His comments and arguments and ideas resonate with me.”

But Harris is going with Clinton, she added, because “there’s a very large segment of the country who’s not anywhere near that yet.”

Stump speeches by GOP presidential candidates reveal that they're already planning for a race against Hillary Clinton in the general election. (Peter Stevenson/The Washington Post)

As important as the Obama coalition was in 2008, there is another bloc of would-be voters that could prove even more decisive on Feb. 1: the 2016 version of that coalition — this cycle’s round of first-time voters.

The Clinton campaign insists it has done legwork with both groups, covering its bases with those who chose Obama in 2008 — and viewing the 2016 electorate as a new, distinct entity.

“The organization is working hard going after everyone who caucused in 2008 and other years as well,” said Jerry Crawford, a prominent Iowa Democrat and Clinton’s political fixer in the state in 2008 and in 2016. “There is nothing secretive about how you do this. It just takes very hard work day in, day out.”

“For us, a vote is a vote. Whether it is a grandmother or a college student, Hillary wants them to caucus for her, and we are trying to organize to make that happen,” he added.

But the Sanders campaign shows signs of advantage in appealing to first-time voters. In the Register poll, Sanders attracts nearly one-third of his support from college towns — and vastly outperforms Clinton among young voters generally. Additionally, the size of his crowds, which have rivaled those of Republican front-runner Donald Trump, demonstrates a level of enthusiasm unmatched by Clinton.

That enthusiasm gap is also reminiscent of 2008, when Obama drew historic crowds and turnout. Several Obama voters supporting Sanders this time said Clinton just doesn’t excite them in the same way.

Obama “just was the kind of guy I could get behind. It’s kind of the same with Bernie now,” said Ryan Hansen, 31, who attended his first-ever caucus for Obama — and decided pretty quickly this year to pass again on Clinton. “He’s the kind of guy who says what he means, and that’s what we want.

“She seems fake,” Hansen added, searching for the words. “And the next-in-line kind of thing. You know what I mean?”

Clinton has paid close attention to the building blocks of Obama’s coalition — including Iowa’s small but growing population of minority voters, which the president activated on his winning caucus night.

In December, Clinton met privately with community leaders in Ottumwa, where the percentage of Hispanic residents is twice that of Hispanics in the state overall. Her campaign also set up a bilingual phone bank there. They have dedicated organizers to turn out African American voters in the three cities with the largest black populations: Waterloo, Davenport and Des Moines.

In addition, her campaign has all but co-opted his most influential endorsers and community activists, including former party chair Sue Dvorsky, Attorney General Tom Miller and State Treasurer Mike Fitzgerald. She also picked up the support of former Iowa state representative Wayne Ford, one of the state’s most prominent African American leaders, following the Iowa Brown & Black Presidential Forum Jan. 11.

In an interview after the forum, Ford said Clinton’s answers on criminal justice reform and the importance of education for minority communities swayed his vote. But asked about what differentiated Clinton from Sanders, Ford said it was really more about timing — about his view that, this year, she is the more qualified to be president.

“If this were a different time in the country,” he said as his voice trailed off. “It’s all about timing. Lincoln was president at the right time. FDR was president at the right time. Obama was president at the right time. I think Hillary will be president at the right time.”

Ford predicted that it will be hard for Clinton on caucus night to replicate Obama’s success dominating the minority vote and drawing out higher-than-expected turnout.

But Sanders faces his own challenges with minority voters. He has struggled to adapt a message focused on economic equality to the concerns of minorities. And the challenge will become increasingly problematic after the first two contests in Iowa and New Hampshire, both predominantly white.

Sanders is less well-known among black voters. And unlike Clinton, he has staked more of his candidacy positioning himself to the left of Obama on issues than on ratifying Obama’s presidency.

Sanders, however, has shown formidable strength among the very elements of the electorate that Clinton’s 2008 campaign and pundits discounted eight years ago: young voters, independents and first-time caucus-goers.

“That was the Obama cocktail that brought in newcomers and blew the top off of many caucus sites with huge turnout,” Iowa pollster J. Ann Selzer said. She conducted the recent Register poll, which shows lopsided support for Sanders over Clinton among those groups.

In 2008, recent college grad Tess Pocock, 25, was too young to cast a vote for Obama, but she pitched in as a volunteer for his campaign. This year, she’s all in for Sanders.

“It seems that Bernie’s always just one step ahead,” Pocock said. “As someone who’s been interested in politics for a while, and being a millennial, I’m just sort of sick of the status quo. That’s sort of what Hillary represents for me.”