WASHINGTON — House Speaker Nancy Pelosi and Senator Chuck Schumer, the minority leader, hear constant warnings from allies about congressional losses in November if the party nominates Bernie Sanders for president. Democratic House members share their Sanders fears on text-messaging chains. Bill Clinton, in calls with old friends, vents about the party getting wiped out in the general election.
And officials in the national and state parties are increasingly anxious about splintered primaries on Super Tuesday and beyond, where the liberal Mr. Sanders edges out moderate candidates who collectively win more votes.
Dozens of interviews with Democratic establishment leaders this week show that they are not just worried about Mr. Sanders’s candidacy, but are also willing to risk intraparty damage to stop his nomination at the national convention in July if they get the chance. Since Mr. Sanders’s victory in Nevada’s caucuses on Saturday, The Times has interviewed 93 party officials — all of them superdelegates, who could have a say on the nominee at the convention — and found overwhelming opposition to handing the Vermont senator the nomination if he arrived with the most delegates but fell short of a majority.
“We’re way, way, way past the day where party leaders can determine an outcome here, but I think there’s a vibrant conversation about whether there is anything that can be done,” said Jim Himes, a Connecticut congressman and superdelegate, who believed the nominee should have a majority of delegates.
From California to the Carolinas, and North Dakota to Ohio, the party leaders say they worry that Mr. Sanders, a democratic socialist with passionate but limited support so far, will lose to President Trump, and drag down moderate House and Senate candidates in swing states with his left-wing agenda of “Medicare for all” and free four-year public college.
Mr. Sanders and his advisers insist that the opposite is true — that his ideas will generate huge excitement among young and working-class voters, and lead to record turnout. Such hopes have yet to be borne out in nominating contests so far.
Jay Jacobs, the New York State Democratic Party chairman and a superdelegate, echoing many others interviewed, said that superdelegates should choose a nominee they believed had the best chance of defeating Mr. Trump if no candidate wins a majority of delegates during the primaries. Mr. Sanders argued that he should become the nominee at the convention with a plurality of delegates, to reflect the will of voters, and that denying him the nomination would enrage his supporters and split the party for years to come.
“Bernie wants to redefine the rules and just say he just needs a plurality,” Mr. Jacobs said. “I don’t think we buy that. I don’t think the mainstream of the Democratic Party buys that. If he doesn’t have a majority, it stands to reason that he may not become the nominee.”
This article is based on interviews with the 93 superdelegates, out of 771 total, as well as party strategists and aides to senior Democrats about the thinking of party leaders. A vast majority of those superdelegates — whose ranks include federal elected officials, former presidents and vice presidents and D.N.C. members — predicted that no candidate would clinch the nomination during the primaries, and that there would be a brokered convention fight in July to choose a nominee.
In a reflection of the establishment’s wariness about Mr. Sanders, only nine of the 93 superdelegates interviewed said that Mr. Sanders should become the nominee purely on the basis of arriving at the convention with a plurality, if he was short of a majority.
“I’ve had 60 years experience with Democratic delegates — I don’t think they will do anything like that,” said former Vice President Walter Mondale, who is a superdelegate. “They will each do what they want to do, and somehow they will work it out. God knows how.”
As for his own vote, Mr. Mondale, the 1984 Democratic presidential nominee, said, “I vote for the person I think should be president.”
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‘I’ve had 60 years experience with Democratic delegates. I don’t think they will do anything like that.’
— Former Vice President Walter Mondale
While there is no widespread public effort underway to undercut Mr. Sanders, arresting his rise has emerged as the dominant topic in many Democratic circles. Some are trying to act well before the convention: Since Mr. Sanders won Nevada’s caucuses on Saturday, four donors have approached former Representative Steve Israel of New York to ask if he can suggest someone to run a super PAC aimed at blocking Mr. Sanders. He declined their offer.
“People are worried,” said former Senator Chris Dodd of Connecticut, a former Democratic National Committee chairman who in October endorsed former Vice President Joseph R. Biden Jr. “How you can spend four or five months hoping you don’t have to put a bumper sticker from that guy on your car.”
That anxiety has led even superdelegates to suggest ideas that sound ripped from the pages of a political drama.
In recent weeks, Democrats have placed a steady stream of calls to Senator Sherrod Brown of Ohio, who opted against running for president nearly a year ago, suggesting that he can emerge as a white knight nominee at a brokered convention — in part on the theory that he may carry his home state in a general election.
“If you could get to a convention and pick Sherrod Brown, that would be wonderful, but that’s more like a novel,” Representative Steve Cohen of Tennessee said. “Donald Trump’s presidency is like a horror story, so if you can have a horror story you might as well have a novel.”
Others are urging former President Barack Obama to get involved to broker a truce — either among the four moderate candidates or between the Sanders and establishment wings, according to three people familiar with those conversations.
William Owen, a D.N.C. member from Tennessee, suggested that if Mr. Obama was unwilling, his wife, Michelle, could be nominated as vice president, giving the party a figure they could rally behind.
“She’s the only person I can think of who can unify the party and help us win,” he said. “This election is about saving the American experiment as a republic. It’s also about saving the world. This is not an ordinary election.”
People close to Mr. Obama say he has no intention of getting involved in the primary contest, seeing his role as less of a kingmaker than as a unifying figure to help heal party divisions once Democrats settle on a nominee. He also believed that the Democratic Party shouldn’t engage in smoke-filled-room politics, arguing that those kinds of deals would have prevented him from capturing the nomination when he ran against Hillary Clinton in 2008.
‘This election is about saving the American experiment as a republic.’
— William Owen, a D.N.C. member from Tennessee
Officials at the Democratic National Committee maintain that it is highly improbable to head to the convention without an assured nominee. Historically, superdelegates had always supported the candidate who won the most pledged delegates, which accrue from primary and caucus wins. While those delegates are proportioned based on the results of those elections, they are not legally bound — meaning that they are technically free to change their votes as the race progresses.
In recent days, both Mr. Biden and Senator Elizabeth Warren of Massachusetts said that Mr. Sanders should not become the nominee if he arrived at the convention short of a delegate majority. “Bernie had a big hand in writing these rules,” Ms. Warren said during a CNN forum on Wednesday night. “I don’t see how he thinks he gets to change them now that he thinks there’s an advantage for him.”
Slightly less than 3 percent of delegates have been allocated in the race so far, and Mr. Sanders, of course, can win a majority, making him the nominee. But while Mr. Sanders has demonstrated momentum in the race, winning the most votes in each of the first three contests, he has yet to show that he can expand his coalition enough to set his campaign on a path to capturing the majority of delegates. As a result, some within Mr. Sanders’s own campaign foresee a possible brokered convention.
The argument of Mr. Sanders and his allies — that a plurality of delegates should be sufficient to clinch the nomination — is a different standard than the one laid out in party rules that his team helped draft two years ago. It’s also a reversal of their stance in 2016, when Mr. Sanders encouraged superdelegates to support him over Mrs. Clinton, who secured the majority of pledged delegates.
“The will of the people should prevail,” he said when asked during last week’s debate if the candidate with the most pledged delegates should be the Democratic nominee. “The person who has the most votes should become the nominee.”
Supporters of Mr. Sanders said that blocking him from the nomination if he had the most delegates would repel progressives, and would deliver a second term to Mr. Trump.
“If Bernie gets a plurality and nobody else is even close and the superdelegates weigh in and say, ‘We know better than the voters,’ I think that will be a big problem,” said Representative Pramila Jayapal of Washington state, a Sanders supporter who is co-chairwoman of the Congressional Progressive Caucus.
‘We don’t have to freak out.’
— Jane Kleeb, the Nebraska Democratic chairwoman
Not only would a messy convention fight risk alienating a sizable part of the Democratic base that supports Mr. Sanders, it would also give Republicans ammunition to use in the general election.
“We don’t have to freak out,” said Jane Kleeb, the Nebraska Democratic chairwoman, who helped write Democrats’ presidential nominating rules and supported Mr. Sanders in 2016. “We shouldn’t be second-guessing voters. If that’s what our party leaders are going to do, you’ll see rebellion not just in the presidential race, but in down-ballot races as well.”
Others in the party view Mr. Sanders as such an existential threat that they see stopping him from winning the nomination as less risky than a public convention fight. Many feared that putting Mr. Sanders on the top of the ticket could cost Democrats the political gains of the Trump era, a period when the party won control of the House, took governor’s mansions in deep red states and flipped statehouses across the country.
“Bernie seems to have declared war on the Democratic Party — and it’s caused panic in the House ranks,” said Representative Josh Gottheimer of New Jersey, a supporter of former Mayor Michael Bloomberg of New York. Private polling of Mr. Gottheimer’s northern New Jersey district, for example, shows a double-digit gap in the approval ratings of Mr. Trump and Mr. Sanders.
Representative Veronica Escobar of Texas said that if Mr. Sanders arrived at the convention with 40 percent of the delegates, it wouldn’t be enough to convince her to vote for him on the second ballot.
“If 60 percent is not with Bernie Sanders, I think that says something, I really do,” she said.
Results in the Super Tuesday contests should give Democrats a strong indication of where the nominating contest is headed.
‘If 60 percent is not with Bernie Sanders, I think that says something, I really do.’
— Representative Veronica Escobar of Texas
Should Mr. Sanders win big in the 16 states and territories holding primaries and caucuses on Super Tuesday next week, he could be on a path to the 1,991 pledged delegates needed to capture the nomination on the first ballot at the party’s convention. But if the Super Tuesday vote is sharply divided among Mr. Sanders and two or more other rivals, the Vermont senator could find himself with more delegates than the competition but not enough to win the nomination outright.
Under the current rules, the convention would then go to a second ballot. On that vote, all 3,979 pledged delegates and 771 superdelegates would be free to vote for any candidate they chose.
That would give Democratic delegates a huge amount of power to determine the nominee, setting off a fierce round of jockeying by the candidates to win over 2,375.5 delegates and superdelegates. (Superdelegates from Democrats Abroad count as half a vote each.)
“It is a mini primary process in the making,” said Leah Daughtry, who ran the party’s 2008 and 2016 conventions. She’s been warning Democratic donors about the prospect of a contested convention for nearly a year. “If you don’t have a political operation that will get you through a second ballot then what are you going to do in a general?”
The campaigns are already strategizing about how they will handle a protracted convention battle. Superdelegates, too, are brushing up on the rules: Ms. Pelosi invited House Democrats to a meeting at D.N.C. headquarters on Thursday to review the details of the convention process.
“Whatever the atmosphere is, and I would hope that everyone would say, no matter who the nominee is for president, we wholeheartedly embrace that person,” she said, in a private caucus meeting on Wednesday morning, according to an aide in the room.
According to a person familiar with the private conversations, Mr. Schumer told people he had so far stayed out of the primary because many members of his caucus were running. He argued that there was one school of thought that you needed to win the base and one that you needed to bring new voters in, and said that he did not yet know which candidate would be able to accomplish those goals.
A number of superdelegates dream of a savior candidate who is not now in the race, perhaps Mr. Brown, or maybe someone who already dropped out the race, like Senator Kamala Harris of California.
Representative Don Beyer of Virginia cast an even wider net, suggesting senators from Virginia and Delaware, along with Ms. Pelosi, as possible nominees.
“At some point you could imagine saying, ‘Let’s go get Mark Warner, Chris Coons, Nancy Pelosi,’” he said, while preparing to introduce the former Mayor Pete Buttigieg of South Bend., Ind., at a campaign event near his home on Sunday. “Somebody that could win and we could all get behind and celebrate.”