DES MOINES — Bernie Sanders examined the butter cow. He power-walked by the Ferris wheel. He gobbled a corn dog.
He spoke to almost no one.
Most presidential candidates use the 10-day Iowa State Fair to showcase their retail campaigning skills, because it is one of the best opportunities to meet a wide cross-section of voters before the caucuses in February. Mr. Sanders’s approach to the event on Sunday — stride briskly, wave occasionally, converse infrequently — underscored how he has grounded his campaign in championing ideas rather than establishing human connections.
His lectern-pounding, impersonal campaign style served him well during his first presidential run, especially here in Iowa, where his near-victory in the caucuses against Hillary Clinton, the former secretary of State, transformed him into a threat for the Democratic nomination.
Yet even as his campaign seeks to project its strength in early primary states, there are signs — in Iowa polls, conversations with local officials and discussion with dozens of voters — suggesting that Mr. Sanders, 77, may be struggling to gain traction in the state that fueled his political rise.
It is a dynamic that was perhaps most evident last weekend at the state fairgrounds: As voters talked up first-time presidential candidates like Senator Elizabeth Warren, Senator Kamala Harris and Mayor Pete Buttigieg of South Bend, Ind., Mr. Sanders was often an afterthought.
Some voters cited Mr. Sanders’s age. Others said they wanted to elect a woman. Many praised his ability to push the party to the left but said it was time for someone else to claim the progressive mantle.
“I’m liking Elizabeth Warren,” said Danielle Hensley, a 22-year-old student from Iowa City, after casting her presidential vote at the fair’s highly unscientific corn kernel poll. Ms. Hensley supported Mr. Sanders in the caucuses four years ago; now, she explained, she sees him as “a 2016 candidate.”
It is still early in the primary season, and Mr. Sanders and his aides dismiss outright any notion that his Iowa campaign has lost momentum, repeatedly asserting that the campaign is well positioned for the long haul. They remain confident that they can energize first-time caucusgoers who were too young to cast their votes four years ago. And they brush off a recent poll that showed Mr. Sanders slipping in the state, saying that it does not capture the views of younger voters, working-class Democrats and others who are not yet paying attention to the race — groups that the campaign sees as a big part of his base.
“We’re feeling really, really good,” Mr. Sanders told reporters after his turn at the fair’s political soapbox. “I think we’re going to win here in Iowa.”
During a conference call with reporters on Monday, Mr. Sanders’s advisers pushed back against doubts about the strength of the campaign, insisting that most polls still have him in second place, and noting that he enjoyed a boost in support in surveys taken after the second Democratic debates. They also maintained that voters trust Mr. Sanders on health care, which his team argues is the most important issue to the electorate.
Mr. Sanders has some significant advantages in the state.
Through the end of June, he had an estimated 7,000 individual donors in Iowa, according to an analysis of campaign fund-raising records by The New York Times, by far the most of any candidate. And he maintains an army of die-hard liberal foot soldiers who are more than eager to propel him to the convention. On Friday, before the state’s annual Wing Ding dinner in Clear Lake when supporters for the various candidates typically gather and chant outside the event as a show of force, Mr. Sanders’s team boasted that their volunteers had instead knocked on every Democratic door in the town. He plans to return to Iowa next week for what will be his eighth trip to the state since announcing his candidacy in February.
But the landscape for Mr. Sanders is vastly different than it was four years ago. Nearly two dozen candidates are now vying for the nomination. And unlike in 2016, when Mr. Sanders was the only candidate with a liberal populist message, there are now many other progressives who have adopted a similar agenda. There is also a surging energy among young activists for diversity, female candidates and generational change.
At the same time, several Iowa Democratic officials said they were miffed by Mr. Sanders’s campaign, which they see as operating as something of a lone wolf.
Jeannine Grady, Democratic chairwoman in Marshall County, where Mr. Sanders defeated Mrs. Clinton in the caucuses in 2016, said Mr. Sanders’s campaign is not following the traditional campaign playbook of staying in close contact with county chairs.
Though running an unconventional, outsider campaign had worked for him in the past, she said, it may not work this time, especially now that his message is no longer novel and voters have so many other candidates on offer.
“I don’t believe it’s possible for him to run an insurgent campaign like he did four years ago,” said Ms. Grady, who caucused for Mr. Sanders in 2016. “Part of being an insurgent is being relatively unknown. He can’t now be unknown.”
Sanders allies say it is precisely that willingness to operate outside the established political system that is part of Mr. Sanders’s appeal, especially for those who believe the current system is broken and requires wholesale change.
Pete D’Alessandro, who ran Mr. Sanders’s Iowa campaign in 2016 and is now a senior adviser, stressed in an interview that the campaign was working behind the scenes to woo voters who had not yet tuned in to the political process.
“If we do as a team what we’re supposed to do each day, we will be in a position to talk to that voter who can’t engage right now when they’re ready to engage,” he said. “Then you’ll see a whole different dialogue going on.”
And he suggested that Mr. Sanders should not be measured by the usual political metrics for success.
“The reason that I’m not concerned is I know at the end of most days, we sit around as a senior staff and we say, ‘We just won today,’” he said.
But if the stakes are high for every presidential candidate in Iowa, they are even more elevated for Mr. Sanders: Many political observers say success for him in 2020 is predicated on a repeat strong performance in the caucuses.
And as he traveled across Iowa ahead of his visit to the state fair, Mr. Sanders declared that he planned to win not just the Iowa caucuses, but the nominating contests in New Hampshire, Nevada and California as well.
Though he has faced some criticism for adhering strictly to his message, it is, perhaps above all, his constancy that has loyal fans still flocking to his events — he had one of the biggest crowds at the fair — and pledging their allegiance.
Waiting to hear Ms. Warren speak at the fair on Saturday, Misty Cornelius, 38, of Des Moines, said she remained “a strong Bernie supporter” — a declaration confirmed by the glittery “Bernie 2020” tattoo she bore on her chest.
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But there were also skeptical voices.
“He’s unrealistic,” said Michael McDonald, 64, of Altoona.
“I like Bernie, but he seems a little too old, honestly,” said Andrew Ball, 22, of Iowa City.
Teresa Brumer, a 51-year-old dental assistant from Urbandale who caucused for Mr. Sanders in 2016, said she wanted see if Mr. Sanders was “the same man as he was four years ago.”
He was, she said after hearing him speak. But she was now also considering Mr. Buttigieg.
Reid Epstein, Lisa Lerer and Thomas Kaplan contributed reporting from Des Moines, Matt Stevens from New York and Rachel Shorey from Washington.