The Working Families Party, the labor-aligned progressive group whose electoral influence has grown since the 2016 election, has endorsed Senator Elizabeth Warren of Massachusetts for the Democratic presidential nomination, a boon to her candidacy as she attempts to position herself as the main challenger to former Vice President Joseph R. Biden Jr.
The party endorsed Senator Bernie Sanders of Vermont during the last presidential cycle, at which time he described Working Families as “the closest thing” to “my vision of democratic socialism.” The group’s endorsement of Ms. Warren on Monday, one of the few by a prominent progressive organization this early in the primary, could turn heads among left-leaning Democrats desperate to defeat Mr. Biden, the more moderate front-runner, in a primary election where their party’s ideological future is at stake.
“If our focus is on victory, we can’t be delusional about it,” said Maurice Mitchell, the Working Families Party’s national director. “You don’t defeat the moderate wing of Democrats through thought pieces or pithy tweets, you defeat their politics through organizing.”
Mr. Mitchell brushed off the possibility that the group’s endorsement would be seen as a sign of a splintering of the progressive left. The vote among “tens of thousands” of party members resulted in a commanding majority for Ms. Warren, a party spokesman said; she received more than 60 percent of the votes on the first ballot.
“Choosing not to make a decision because of risk or fear of backlash is an abdication of our responsibility, and I’m not willing to do that,” Mr. Mitchell said.
Ms. Warren is coming off a debate performance last week that was generally well received, and she is preparing for a rally in New York on Monday that could be among the largest gatherings for any candidate this year. Mr. Sanders’s campaign shook up its New Hampshire staff over the weekend as Ms. Warren continues to make inroads among progressives.
Also on Monday, Ms. Warren unveiled a plan to combat corruption in government, a core theme of her campaign. The plan is based on a wide-ranging anticorruption bill that she first proposed last year and is a cornerstone of her stump speech on the campaign trail.
Mr. Mitchell and other leaders from the Working Families Party said in interviews that their endorsement came with a message to other progressive organizations. Rather than passively observe the primary, they said, these groups should choose a side and flex their organizing muscle during the early stages to help knock Mr. Biden off his perch.
“Senator Warren knows how to kick Wall Street kleptocrats where it hurts, and she’s got some truly visionary plans to make this country work for the many,” Mr. Mitchell said. “We need a mass movement to make her plans a reality, and we’re going to be a part of that work.”
Traditional bellwether endorsements from labor unions like American Federation of Teachers and the Service Employees International Union have not yet materialized, though Mr. Sanders picked up an endorsement from the United Electrical workers in August. With less than five months to go before the Iowa caucuses formally begin the presidential nominating contest, many organizations are still wrestling with a sprawling Democratic field.
Mr. Sanders finished second in the Working Families Party’s ranked-choice voting system between five candidates — Mr. Sanders, Ms. Warren, the former housing secretary Julián Castro, Senator Cory Booker of New Jersey, and Mayor Bill de Blasio of New York, who held in-person question-and-answer sessions with party members. Senator Kamala Harris of California was dropped from consideration after she canceled her session in August.
Most national polls of the Democratic primary show an increasingly clear top tier of three candidates — Mr. Biden, Ms. Warren and Mr. Sanders — though Mr. Biden has remained the front-runner.
“There will be a point when progressive voters have to make a choice between the candidates running — for some that’s today, and for others that will be on caucus or Primary Day next year,” said Yvette Simpson, chief executive of Democracy for America, another progressive group that endorsed Mr. Sanders four years ago. Ms. Simpson said her group did not plan to endorse a candidate before December.
“There are some great arguments for progressives rallying around a single candidate as soon as possible and others for taking the time to see how the contest develops,” she said.
In the years since President Trump’s election, candidates backed by the Working Families Party have won congressional, state and local races across the country, expanding the group’s power base from the Acela corridor to the West Coast.
Mr. Mitchell took over as national director for the party in 2018, after he rose in prominence during the Black Lives Matter movement born out of protests in Ferguson, Mo.
The group’s leaders stressed that, even with their endorsement, their intention was not to divide the progressive left between Ms. Warren and Mr. Sanders. The senators are longtime friends and have painted themselves as publicly supportive of each other’s candidacies.
“I’m with Bernie,” Ms. Warren said at a Democratic debate over the summer, indicating she supported Mr. Sanders’s single-payer health care plan and signaling their closeness at a time when political observers were craving an intraparty fight.
Still, some more moderate Democrats have continued to sound alarms about progressives’ ability to beat Mr. Trump, and Ms. Warren’s chances in particular. And many Republicans see the embrace of a single-payer, “Medicare for all” health care system and ambitious climate proposals like the Green New Deal as general-election liabilities waiting to be exploited.
Surrogates for other candidates — like Mr. Biden, Ms. Harris and Mayor Pete Buttigieg of South Bend, Ind. — have tried to paint Ms. Warren and Mr. Sanders as candidates of the elite, who talk about lofty ideologies instead of pragmatic solutions.
“My concern about the vision from the Sanders-Warren approach is that it can polarize Americans, when we have other ways to deliver bold solutions without dividing the American people further,” Mr. Buttigieg said Sunday on CNN.
But Mr. Mitchell said he believed the Working Families Party could convert Democrats skeptical of wide-reaching progressive policies.
“I’m not worried about converting people who are already committed to a structural change agenda,” Mr. Mitchell said. “I’m worried about the people who are still trying to figure out where they land.”
Thomas Kaplan contributed reporting.