Ms. Warren garnered 22 percent in a New York Times/Siena College poll, to 19 percent for Bernie Sanders. Pete Buttigieg has surged, while Mr. Biden’s travails have put the race in flux.
The top Democratic presidential candidates are locked in a close race in the 2020 Iowa caucuses, with Senator Elizabeth Warren slightly ahead of Senator Bernie Sanders, Mayor Pete Buttigieg of South Bend, Ind., and former Vice President Joseph R. Biden Jr., according to a New York Times/Siena College poll of likely Democratic caucusgoers.
Ms. Warren appears to have solidified her gains in the first voting state while Mr. Buttigieg has climbed quickly to catch up with Mr. Sanders and overtake Mr. Biden, the onetime front-runner. Ms. Warren is drawing support from 22 percent of likely caucusgoers, while Mr. Sanders is at 19 percent, followed by Mr. Buttigieg at 18 percent and Mr. Biden at 17 percent.
The survey is full of alarming signs for Mr. Biden, who entered the race in April at the top of the polls in Iowa and nationally. He is still in the lead in most national polls, but his comparatively weak position in the earliest primary and caucus states now presents a serious threat to his candidacy. And Mr. Biden’s unsteadiness appears to have opened a path in the race for other Democrats closer to the political middle, particularly Mr. Buttigieg.
The poll reveals a race in flux but not in disarray, framed by a stark debate about the direction of the Democratic Party and by a degree of fluidity arising from Mr. Biden’s travails. In the early states, at least, the former vice president appears to be buckling on one side to the expansive populism of Ms. Warren and Mr. Sanders, and on the other to Mr. Buttigieg’s calls for generational change.
While no single candidate has a decisive advantage, the strongest currents in the party appear to be swirling around candidates promising in different ways to challenge the existing political and economic order.
Several of them would also represent change by virtue of their identities, including Ms. Warren, who would be the first female president, and Mr. Buttigieg, who is gay. But despite the historic diversity of the field, all the top candidates are white. In Iowa, a state that helped vault Barack Obama into the presidency, the poll found a substantial bloc concerned that anyone other than a heterosexual white man might struggle to defeat President Trump.
The survey found Iowa Democrats in a divided and perhaps indecisive state about what the party must do in order to deny Mr. Trump a second term. They are an ideologically mixed group, with younger voters trending to the left and leaning strongly toward Ms. Warren and Mr. Sanders. Mr. Biden remains the favorite candidate of older voters, but only 2 percent of respondents under 45 years old said they currently plan to caucus for him.
In the poll, large majorities were supportive of ambitious liberal policy goals, like breaking up big banks, increasing Social Security benefits and implementing single-payer health care. But perhaps out of political caution, the poll also found that more Democrats would prefer to nominate someone who supports improving the private health insurance system rather than replacing it altogether. And most Democrats said they would favor a nominee willing to work with Republicans.
There is still plenty of room for shifts in political momentum: Two-thirds of likely caucusgoers in The Times poll said they could still be persuaded to change their minds.
Outside the top tier of four candidates, the best-performing Democrat was Senator Amy Klobuchar, supported by 4 percent of respondents, followed by Senator Kamala Harris and Andrew Yang, both at 3 percent, and Senator Cory Booker, Representative Tulsi Gabbard and Tom Steyer, all at 2 percent.
Factoring in voters’ second choices, which can play a key role in the complex caucus process, Ms. Warren had the broadest appeal: She is the first or second preference of 47 percent of Iowa Democrats, with two-thirds of Sanders supporters naming her as their backup choice.
Mr. Sanders is the first or second choice of 34 percent of likely caucusgoers, followed by Mr. Buttigieg at 31 percent. Mr. Biden was in fourth place by this measure, at 28 percent; only 1 in 10 voters named him as their second choice.
The Times/Siena survey of 439 Iowa Democratic caucusgoers was conducted from Oct. 25-30 and has a margin of error of plus or minus 4.7 percentage points.
One issue that occasions little division among Democrats is impeachment. Eighty-nine percent of people in the poll said they support impeaching Mr. Trump and removing him from office.
Most Iowa Democrats in the poll said they were somewhat or very confident that the party’s top candidates would beat Mr. Trump in the general election. There was no difference in how they assessed Mr. Biden and Ms. Warren on that measure, and Mr. Sanders and Mr. Buttigieg fared only slightly worse.
The confidence Iowa Democrats expressed in Ms. Warren as a general-election candidate could represent something of a turning point for her candidacy, if she can extend the sentiment to other early states. For much of the race, even Democratic voters who have embraced her ideas and political persona have harbored reservations about her odds against Mr. Trump. In Iowa, that appears to have changed.
Jonathan Morrison, 45, of Mason City, said he was drawn to Ms. Warren because of her grasp of economic issues and believed she would “hold her own” against the president.
“I don’t think she’s going to allow herself to be pushed around or bullied by Trump,” he said. “She’s going to stick to the facts and call him out on his policies.”
Mr. Morrison, who said he is a drone pilot in the oil and gas industry, said he also liked Mr. Buttigieg, whom he described as having a “leadership aura about him.”
“I think Pete Buttigieg is going to be president someday,” he said. “I’m not sure it’s this time around.”
Both Ms. Warren and Mr. Sanders appear to be tapping into a thirst among many primary voters for transformational policies rather than incremental improvements in governance. But the presence of two forceful, well-funded populists in the race may be preventing either Mr. Sanders or Ms. Warren from gaining a wide advantage.
They have assembled somewhat different political coalitions: Ms. Warren is the top choice of younger voters, women and people with college degrees, while Mr. Sanders fares better with men and people with high school degrees or less. He also retains significant backing from young people, and his supporters are the least likely to say they might change their minds before February.
Though Mr. Buttigieg would be the youngest president ever, he is not exceptionally popular with his generational cohort. He fared somewhat better with older voters than younger ones; like Ms. Warren, he registered strongly among people with college and postgraduate degrees.
Mr. Biden’s support comes almost exclusively from older voters: Among people 65 years or older, he is still the front-runner, with backing from nearly a third of them. But he has negligible support among younger Iowans. With voters under 45, Mr. Biden is polling several points behind Mr. Yang, a former tech executive who has never run for office before.
An ideological gulf, running along generational lines, is a major feature of the Democratic race. Two-thirds of voters under 30 favored either Ms. Warren or Mr. Sanders, while a smaller majority of people over 65 favored either Mr. Biden or Mr. Buttigieg.
An overwhelming 85 percent of voters under 30 said they preferred a nominee promising fundamental change over one seeking to restore normalcy in Washington. Among voters more than 65 years old, 7 in 10 preferred a candidate who would bring back normalcy.
William Nix of Waterloo, Iowa, is among the young voters torn between several candidates promising large-scale change. He said he had long admired Mr. Sanders but worried that he might pull out of the race after his recent heart attack. Mr. Nix, who is 21 and works on an assembly line at John Deere, said he was considering Ms. Warren and Mr. Buttigieg, and wanted a nominee focused on economic inequality and access to education.
“I’m really all for making going to college more affordable,” Mr. Nix said. “That is my biggest thing, because I want to go to college myself.”
Most Iowa Democrats appear to believe it is easier for candidates who are heterosexual, white, male and ideologically moderate to win presidential races, though that assessment is not playing a decisive role in shaping their caucus preferences. Most poll respondents said they believed it would be harder to win the election with a nominee who is more liberal than most Democrats, or one who is gay. About half expressed those reservations about a female nominee, and 4 in 10 were pessimistic about an African-American candidate
These reservations about embracing the diversity of their presidential field have not translated into enthusiasm for Mr. Biden. One reason may be his age: A majority of respondents said they believed it would be harder to win the election with a candidate over the age of 75.
Both Mr. Biden and Mr. Sanders would turn 80 within a year or two of taking office.
Julia Roberts, a voter in Winterset, Iowa, is among those wary of nominating someone whose identity could unsettle rural conservatives. Ms. Roberts, 60, a retired state employee, favored Mr. Biden because she saw him as the strongest general-election candidate and valued his foreign policy experience.
“I think, really, he’s got the best chance of beating Trump,” Ms. Roberts said, adding that she also liked Ms. Warren and Mr. Buttigieg but feared there would be “prejudice in play” against them.
Tonda Hadden, 63, of Council Bluffs, Iowa, said she had originally favored Mr. Biden or Mr. Sanders. But she worried Mr. Sanders was “too old and too left.” With Mr. Biden, she had grown “a little worried about his gaffes.”
Ms. Hadden said she was now “still looking” over her options: She named Ms. Warren as her current favorite and Mr. Buttigieg as an intriguing alternative. And she said she hoped some others, like Mr. Booker, whom she saw interviewed Wednesday on “The View,” would get a closer look from voters.
“I really like him,” she said of Mr. Booker, “and I don’t understand why he’s not up in the polls.”