DES MOINES — Iowa Democrats are displaying far less passion forHillary Clinton than for Senator Bernie Sanders of Vermont three weeks before the presidential caucuses, creating anxiety inside the Clinton campaign as she scrambles to energize supporters and to court wavering voters.
The enthusiasm gap spilled abundantly into view in recent days, from the cheering crowds and emotional outpourings that greeted Mr. Sanders, and in interviews with more than 50 Iowans at campaign stops for both candidates.
Voters have mobbed Mr. Sanders at events since Friday, some jumping over chairs to shake his hand, snap a selfie or thank him for speaking about the middle class. “Did you get to touch him?” asked one woman who could not get close enough after an event here on Saturday.
“We love you, Bernie! Enough is enough!” Nathan Arentsen, 29, cheered several times at another event in Des Moines as he stomped his feet to signal support for the candidate.
Audiences for Mrs. Clinton have yet to grow to consistently match those for Mr. Sanders, and the typical reception for her was evident on Monday in Waterloo. About 300 people welcomed Mrs. Clinton enthusiastically and listened to her diligently, but many of them, still unsure, rebuffed Clinton aides trying to get them to sign “commitment cards” to caucus for her.
“I personally want to find out if she’s trustworthy or not,” said Katie Bailey, 71, of Cedar Falls. “There’s so much un-trust. I want to eyeball her.”
Matt Fagerlind, 36, also attended Mrs. Clinton’s Waterloo event, but he found himself thinking about how Mr. Sanders’s rallies had the same uplifting emotional intensity as Barack Obama’s in 2008. “I think Sanders is going to give her a good run,” he said, describing himself as unmoved by Mrs. Clinton and planning to vote for Mr. Sanders.
(Ultimately, a Clinton aide said, about half of the audience signed commitment cards.)
With a major new poll showing Mr. Sanders closing within three points of her in Iowa, Mrs. Clinton and her aides have dropped any pretense that they can ignore Mr. Sanders or treat him like a gadfly. They have become zealous and combative as they try new ways to undercut his high favorability ratings.
On Monday, Mrs. Clinton proposed raising the income tax by four percentage points for people earning more than $5 million a year, an idea virtually out of the Sanders playbook. At the same time, she is going hard on the offensive on gun control and health care, undertaking relentless attacks on Mr. Sanders that can feel somewhat forced, like portraying him as an ally of the National Rifle Association. To amplify her criticisms, she has even taken to calling in to MSNBC news shows that are popular with Mr. Sanders’s liberal base, a level of engagement with the news media that she has rarely displayed, especially with erstwhile critics like Chris Matthews.
She is also increasingly trying to tap into the popularity of President Obama and former President Bill Clinton after insisting for months that she was not running for a third term for either man. She held her Waterloo event with Mr. Obama’s transportation secretary, Anthony Foxx, a North Carolina politician whose endorsement had little resonance here, other than his ties to the president. And Mr. Clinton is being dispatched to Iowa on Friday for his second campaign swing in two weeks.
Clinton advisers said they believed Iowa was a single-digit race and have been warning supporters against complacency, admitting that Mr. Sanders’s operation in the state was better financed and organized than they had expected. On Saturday, they began trying to undercut his electability with a television ad casting Mrs. Clinton as the strongest possible Democratic nominee, even though some polls show Mr. Sanders would perform well in matchups against Republicans like Donald J. Trump and Senator Ted Cruz of Texas.
A Sanders victory in Iowa would be a shock given the institutional advantages held by Mrs. Clinton, a former secretary of state and a favorite of the Iowa Democratic establishment. It would also set off significant momentum for Mr. Sanders heading into the Feb. 9 primary in New Hampshire, where he is well known as a senator from neighboring Vermont and holds a slight lead in the polls.
Several of Mrs. Clinton’s advisers, speaking on the condition of anonymity to discuss the race candidly, said that they were anxious but not panicking about Iowa, saying that they believed she would still deliver a victory here.
Still, some advisers said they were torn about whether the campaign would ultimately regret purposely holding small events in Iowa — a strategy Mrs. Clinton preferred — given Mr. Sanders’s ability to continue to turn out and energize huge crowds, which they had not anticipated.
Some members of her Iowa team, however, said they were confident that passion for Mrs. Clinton was intensifying.
“It’s something that’s growing closer to caucus day,” said Kane Miller, the Clinton campaign’s organizing director for Polk County, which includes Des Moines. Sitting in a regional field office adorned with signs reading “Leave No Doubt” to inspire campaign workers to fight for every last vote, Mr. Miller said, “This previous weekend was negative degrees, and 80 percent of people confirmed to volunteer were out knocking on doors. That’s a great measure of enthusiasm.”
Both Mr. Sanders and Mrs. Clinton garnered several rounds of applause on Monday night at the Brown and Black Forum at Drake University here, though the crowd seemed more delighted with Mr. Sanders as he denounced a 51 percent unemployment rate for black men with a high school education and joked that he would consider living in the White House to be public housing.
The warmth for Mr. Sanders was notable because of Mrs. Clinton’s historical popularity among minority voters, particularly African-Americans. Mrs. Clinton drew cheers as well for saying she would not use the term “illegal immigrant” and for pledging to help Central American countries stem the violence that people there flee.
Although crowds and excitement in Iowa have been perceptibly greater for Mr. Sanders than for Mrs. Clinton, polls present a mixed picture. A new NBC/Wall Street Journal/Marist poll, the one reporting a three-point race in Iowa, also found that 76 percent of Clinton backers “strongly support” their candidate, compared with 66 percent of Sanders voters. Another poll, by Quinnipiac University in mid-December, found that very liberal Iowans were the most enthusiastic about the election, and that Mr. Sanders was the favorite among these voters.
Clinton advisers pointed to the NBC poll as evidence of passion for Mrs. Clinton, while Sanders advisers argued that it reflected dutiful support among her admirers rather than the level of excitement that helps ensure people show up to caucus.
The Clinton campaign still has significant structural advantages in Iowa to help turn out caucus voters. The state’s most popular Democrats have endorsed Mrs. Clinton, including former Senator Tom Harkin and former Gov. Tom Vilsack, helping her leverage their political networks. She also has endorsements from several unions and groups like the Planned Parenthood Action Fund.
Advisers say they have strong organizations in the most populous counties and have compiled data on tens of thousands of Democrats, many of whom who are receiving phone calls or visits from teams of volunteers who crowd field offices like Mr. Miller’s. Mrs. Clinton’s campaign manager, Robby Mook, is also a veteran of caucus contests, while strategists like Joel Benenson were part of Mr. Obama’s campaign in 2008.
Some Iowans backing Mr. Sanders believe that polls are underestimating his strength, given the minute-to-minute intensity of adoring messages about him on Twitter and other supportive comments he receives on social media. Mr. Sanders has more than 14,000 volunteers in Iowa, and he has spoken to more than 40,000 people at events in the state so far, huge numbers that include young people, independents and new voters who might not be on pollsters’ call sheets. (Mrs. Clinton’s advisers declined to say how many volunteers she had or people she had spoken to in Iowa.)
“I think his secret weapon, maybe his silver bullet even, is the young adult population that hasn’t been involved in politics up until this point,” said Katie Mitchell, 28, a middle school teacher who lives in Des Moines.
Mrs. Clinton’s campaign is trying to shore up her base among female voters: Lena Dunham, the star of the HBO series “Girls,” was deployed on Saturday to make a feminist pitch for Mrs. Clinton to crowds of mostly young women in Iowa City and Des Moines. Yet many younger women who gathered did not share Ms. Dunham’s visceral enthusiasm for Mrs. Clinton, saying that for most of their lives she has been a familiar fixture of establishment politics rather than an exciting new voice or an agent of change.
“Bernie Sanders feels new, and Hillary seems like a Washington insider,” said Laura Cornell, 17, who was encouraged by friends to hear Ms. Dunham’s pitch but remained committed to Mr. Sanders.
Many of the Sanders supporters interviewed said they felt personally moved by his message and by what they saw as his sincerity. Bert Permar, 86, a retired professor, said he had gone to four Sanders events and was now making calls to share the candidate’s message about tackling wealth disparities in America.
“I love to see him. He motivates me,” Mr. Permar said on Sunday, sitting in the front row at a Sanders forum on veterans’ issues in Marshalltown. “I get emotional. It brings tears that someone is talking about the issues that we should be concerned about.”