BETTENDORF, Iowa — As they streamed out of the ballroom following a Scott County fund-raising banquet Saturday night, one after the other Iowa Democrats admitted that they still had not decided whom to support just over a week before the state’s presidential caucuses.
But by not mentioning his name as they rattled off their short lists, they made it clear whom they would not support: Senator Bernie Sanders, the democratic socialist from Vermont who has taken the lead in recent polls.
Instead, every one of the 30 still-undecided Democratic activists here rattled off some combination of the same four names — Senators Elizabeth Warren of Massachusetts and Amy Klobuchar of Minnesota, former Vice President Joseph R. Biden Jr. and former Mayor Pete Buttigieg of South Bend, Ind.
As Mr. Sanders tightens his grip on the party’s young and left-wing voters in Iowa, more traditional Democrats, the ones who happily sit through marathon banquet dinners to hear the candidates and their representatives, remain split between his four leading competitors or remain unsure altogether about whom to rally behind.
“I have told my colleagues all along: Bernie Sanders can win with 27 percent of the vote here,” said Representative Dave Loebsack, an Iowa Democrat supporting Mr. Buttigieg, alluding to his fellow lawmakers, many of whom are deeply uneasy about running with Mr. Sanders on top of the ticket.
The fracture among mainstream Democrats here carries profound implications for a primary that has already unsettled the party establishment and prompted late entrants into the race.
Mr. Sanders is threatening to seize control in the early states, taking narrow but clear polling leads in Iowa and New Hampshire and increasingly menacing Mr. Biden’s advantage in national polls. With his mammoth online fund-raising operation, Mr. Sanders appears to be in a position of financial strength unmatched by any other candidate besides Michael R. Bloomberg, the billionaire former mayor of New York City.
Mr. Sanders’s endurance, and his apparent rise in the earliest primary and caucus states, reflects both the loyalty of his core supporters and their conviction that Mr. Sanders would bring the same fighting resilience to the general election. But even among many liberals who admire Mr. Sanders’s campaign, or some of his policy ideas, there is deep concern about the implications of nominating a candidate from the left whom President Trump is sure to portray as extreme.
“I think that Bernie is just a bridge too far for the country,” said Bonnie Campbell, a former Iowa attorney general who is supporting Mr. Biden. Ms. Campbell said she would have no difficulty supporting Mr. Sanders in the general election, but added, “I can tell you, I hear from friends and colleagues who say: ‘Oh my God, what are we going to do if Bernie wins?’”
But in Iowa, Democrats who hope to avert that outcome do not appear close to settling on another candidate as an alternative to Mr. Sanders. And if more moderate voters don’t coalesce behind an alternative by next week’s caucus, party traditionalists fear, Mr. Sanders could win Iowa with only a modest plurality, emboldening his leading rivals to remain in the race, and then notch another victory again a week later in New Hampshire. No Democrat in modern times has lost contested races in both Iowa and New Hampshire and claimed the nomination.
The early primary and caucus outcomes could have an outsize impact on later primaries, including the large states voting in March, some of which begin collecting mail-in and early ballots in the immediate aftermath of Iowa. If a candidate like Mr. Sanders were to seize momentum next week, it could help him build a head start in states like California and Texas.
It is a scenario that is deeply alarming to establishment-aligned Democrats, if not unfamiliar. Four years ago, convinced Donald Trump could not win the presidency, they watched with delight as he snatched the Republican nomination without winning majorities because his more traditional rivals divided the vote and refused to bow out.
The Democrats in this race have been as reluctant to target Mr. Sanders as the Republicans were to target Mr. Trump four years ago; in each case they were skeptical of his staying power and believed they had more to gain by attacking other rivals.
Even now, as Mr. Sanders takes a lead in the first two early states, his opponents have not delivered a sustained argument against his candidacy, and remain reluctant to take him on: while Mr. Buttigieg drew attention for warning in a fund-raising solicitation that a Sanders nomination would be too risky, he notably declined to amplify his rhetoric in television interviews over the weekend. The closest he has come to confronting his rival on the left is to make oblique references to the often-bitter 2016 primary between Hillary Clinton and Mr. Sanders.
“Most of us would agree the less 2020 resembles 2016 the better — in all respects,” Mr. Buttigieg said in a brief interview. Each of the would-be Stop Sanders candidates has built enough political strength to justify forging ahead: Mr. Biden remains the national front-runner, with unmatched support among black voters; Mr. Buttigieg and Ms. Warren both have double-digit support in New Hampshire polls, and sizable war chests; Ms. Klobuchar has the thinnest operation beyond Iowa of the group, but over the weekend she earned the endorsement of New Hampshire’s influential Union Leader newspaper.
Should all four move forward from Iowa, with their perceived strengths and weaknesses, it could make it difficult for any of them to become a rallying point for voters uneasy about Mr. Sanders.
Complicating matters further for traditionalists, and making this race potentially even messier than Mr. Trump’s primary, is the presence of Mr. Bloomberg, who is not contesting the traditional early states in February but has already poured more than $270 million in advertising into later contests and made clear to allies that he will remain in the race should Mr. Sanders come roaring into March.
Mr. Bloomberg was on Ms. Klobuchar’s mind as she left the dinner here Saturday. She was asked if she would remain in the race if she did not break into the top three in the caucuses, which has often been the number of viable candidates who leave the state.
Even if you’re in fourth, she was asked?
“You think it’s only going to be down to four candidates even by New Hampshire?” she said before answering the question. “No, it’s not.”
Then, pointing to Mr. Bloomberg, she explained why the Democratic vote may remain splintered.
“Why would I get out while he’s still in?” Ms. Klobuchar demanded.
With nearly 40 percent of Iowa voters indicating in a new New York Times-Siena College poll that they were still not certain about whom to support, Mr. Sanders could still suffer a reversal of fortune here.
That’s in part because of the state’s complex, multiphase caucusing process, which allows supporters of underdog candidates to shift to stronger contenders. If Mr. Sanders has the most enthusiastic base of support in Iowa, he may be less well positioned to expand his bloc in later rounds should moderate voters rally to one of the four other leading candidates.
And it’s Ms. Klobuchar whom Iowa Democrats are watching most closely. If she does not reach 15 percent in most precincts, her supporters could determine the statewide winner if they migrate mostly to one candidate.
Former Gov. Tom Vilsack of Iowa, Mr. Biden’s most prominent supporter in the state, was blunt about why Ms. Klobuchar’s backers should support the former vice president.
Mr. Biden has the best chance of winning the general election, he shares Ms. Klobuchar’s pragmatic politics and “Joe is going to need a running mate,” Mr. Vilsack said.
A more urgent concern for Mr. Vilsack was the prospect of Iowa producing a muddled result, a scenario that’s more likely this year because the state party, for the first time, is releasing raw vote totals from the initial round of balloting as well as the final results and delegate allocations.
“If I had to make one prediction, there will be a split decision and that’ll have repercussions,” he said. “Because whoever quote-unquote wins can claim that they won, and talk about it going into New Hampshire.”
So while they still hope to best Mr. Sanders in Iowa or New Hampshire, several of Mr. Sanders’s rivals have begun emphasizing their strengths in states later in the calendar.
Mr. Biden’s advisers and surrogates have been stressing his support among minority communities that become important starting with the Nevada caucuses on Feb. 22, while Ms. Warren’s campaign circulated a memo last week detailing its preparations in the March primaries that will award most of the delegates that will settle the Democratic nomination.
And in a conversation with volunteers before a town hall-style meeting in Davenport on Sunday, Ms. Warren reiterated her determination to compete into March and beyond, telling supporters she already has staff in 30 states, according to a volunteer who attended the meeting and spoke on the condition of anonymity.
“We all know that this is very likely to be a long nomination process,” said California Assemblyman David Chiu, who on Sunday was opening a campaign headquarters in San Francisco for Ms. Warren and said of her campaign: “They are going to put up a tremendous fight here in the state.”
That phase of the race is also when Mr. Bloomberg, with his vast personal fortune, could become a more urgent factor, either rising as an obstacle for Mr. Sanders or further fracturing the party’s moderate wing.
In California, Mayor Robert Garcia of Long Beach, who endorsed Mr. Biden this month, said he expected the former vice president to consolidate support there “once it becomes clear that there’s a few candidates left.”
But gathering support around just a few candidates could also be difficult in California, Mr. Garcia noted, because the state’s mail-in ballots would list the names of candidates who falter or withdraw over the course of February.
“There are going to be a lot of candidates in California, because they are going to be on the ballot,” he said. “There will be some drop-off, but they’re all competitive here and that’s going to continue.”