DES MOINES, IOWA — Gail Klearman should be a perfect target for Bernie Sanders.

The 56-year-old legal aid attorney caucused for Barack Obama in 2008, and her politics put her more in line with Sanders than with Democratic frontrunner Hillary Clinton. Her children, she said, "feel the Bern."

But Klearman plans to caucus for Clinton in February.

"I think she has a better chance of winning, and I really want to see a Democrat as president," Klearman said after listening to Sanders speak at a Jewish Federation forum in Waukee on Sunday. "I think Americans fear socialism, even though the things that Sen. Sanders is talking about — apparently I agree with him on more issues than I do with Hillary. But not by a whole lot."

The question of whether America is ready to elect its first socialist president is one of two major concerns about Sanders that Iowans raised in interviews with Vox at a half-dozen of his events this past weekend. The other is whether he could govern effectively. Together, they represent the main challenge to Sanders's viability: Even some of the Democrats who think he's on point aren't at all sure he's their best pick to win the presidency or to run Washington.

"Bernie does not say anything I don't like," said John Ross, 76, who came to see Sanders on the stump at the Latino Heritage Festival here on Saturday. "My concern is him being able to win the support he needs in Congress."

The good news for Sanders — who now leads Clinton in New Hampshire and has closed in on her in Iowa and nationally — is that negative messages about Clinton are permeating the Democratic electorate. The bad news is that he hasn't turned Democrats against her the way Obama did in 2008, and he hasn't fully made the sale for himself yet.

Contrasting with Clinton

Sanders's task has three parts — and failure on any single one of them could doom his campaign: He has to convince Democrats that he's much closer to their values than Clinton is, that his chances of winning a general election are at least as good as hers are, and that he would be better than Clinton at implementing the agenda Democrats want in Washington.

In contrasting their records, Sanders, who has been in Congress for almost a quarter of a century, emphasizes his "no" votes: the Iraq War, the bank bailout, the Patriot Act, and a series of trade deals. And his decision to fund his candidacy through small donors rather than ally with a Super PAC also helps him show his backers he's a different kind of Democrat.

Maria Alcivar, a 27-year-old graduate student at Iowa State University, made the trip Sunday to see Sanders at Creative Visions, a community agency that works with at-risk kids in a poverty-plagued section of Des Moines. She said afterward that she'll caucus for him in February because "he's coming from the ground up, without any corporations," while Clinton "has a lot of private prison corporations backing her campaign."

But the contrasts are also perilous for Sanders for two reasons: They risk tarnishing the brand he's built as a rare-breed politician who won't sling mud, and it's hard to square his record of voting no and his no–Super PAC campaign with the idea that he could win the general election and actually implement change in Washington.

Already, Clinton allies privately grouse that Sanders and his supporters are getting away with attacking her while presenting him as pristine. It's only a matter of time before those stories start appearing in print and on television — especially because a pro-Clinton group got hammered for passing an opposition research document to the Huffington Post. And Sanders well understands how important his purity on negative politics is: He had one of his best fundraising hauls after the Huffington Post story.

But he may have to sharpen contrasts with Clinton — to turn more Democrats against her — to make the case that he'd be a better nominee and president. Sanders will have to decide whether it's worth risking his brand to do that.

The Obama experience

The Obama experience seems to be weighing on the minds of Democratic voters in Iowa. In 2008, they took a chance on the candidate who stole their hearts by promising to bring a new brand of politics to Washington. They got their president, but they didn't get all the change they signed up for.

Now Sanders, far more charismatic on the campaign trail than Clinton, is calling on Democrats in Iowa and elsewhere to join in what he calls a political revolution. He stands firmly to the left of Obama and offers them not compromise with Republicans but the alternative path of first electing him and then putting their own shoulders into the work of pressuring Washington from the outside. Obama did some of that, too, but his Organizing for America effort sputtered when it became clear that most voters wanted him to do the heavy lifting after he won.

The brick wall Obama ran into after Democrats lost control of the House in the 2010 midterm election helps explain why some of the Democrats who like Sanders aren't convinced he has what it takes to accomplish what he's promising on the stump.

"It's a question of whether he can get those things done in this divided Congress we have," Lloyd Levine said after Sanders's appearance at the Latino Heritage Festival.

"What's the difference between a liberal and a socialist?"

Sanders has long described himself as a socialist or a democratic socialist, and the potential for that to alienate general election voters is clearly on the minds of Iowans. Sanders was asked about it on Sunday at the town-hall-style meeting with the Jewish Federation.

"In your understanding, what's the difference between a liberal and a socialist?" the event's moderator asked.

"To me, when we talk about Democratic socialism what it means is having a government that represents the vast majority of the people, not just wealthy campaign contributors and corporate America," Sanders said. "It means making sure we guarantee for all of our people basic rights. The right to nutrition. The right for elderly people to have the medicine they need in order to stay alive. That is what democratic socialism means — the rights of people to enjoy the basic necessities of life." And, he added, pointing to public benefits in Scandinavia and Germany, "this is not some kind of revolutionary left-wing idea."

Most Democrats — 59 percent, according to a Gallup poll earlier this year — would consider voting for a socialist candidate. But the general electorate is less sure, at 47 percent. What's clear is that Sanders still has work to do to convince some Democratic voters that the socialist label won't come back to haunt them if they nominate him.

Dennis and Jana Root of Mason City liked what they heard from Sanders in the loosely packed auditorium at Northern Iowa Area Community College, less than an hour from the Minnesota border, Sunday night.

With the blood-red beginnings of a lunar eclipse ultra-clear in the sky over the cornfields outside, Jana Root said it "would be heaven" if Sanders and Clinton were on the Democratic ticket together. But Dennis Root said Sanders has a labeling problem that could really hurt Democrats in the 2016 general election.

"The word 'socialism' is not the way we should talk about Bernie," he said. "I think she’s [Clinton is] more electable."