The Center for Popular Democracy Action, a collective of progressive community groups, is endorsing Mr. Sanders over Elizabeth Warren for the Democratic presidential nomination.
Senator Bernie Sanders spoke at a rally in Cedar Rapids, Iowa, on Saturday.Credit…Jordan Gale for The New York Times
The Center for Popular Democracy Action, a coalition of more than 40 progressive community groups totaling about 600,000 members, will on Tuesday endorse Senator Bernie Sanders of Vermont for the Democratic presidential nomination, signaling that Mr. Sanders’s political standing among the party’s left wing has rebounded — or even risen — in the months since he suffered a heart attack.
At the time of his hospitalization, in early October, Mr. Sanders was under intense political pressure. Senator Elizabeth Warren of Massachusetts had surged past him in polling and positioned herself as the progressive standard-bearer in the race, buoyed by an endorsement from the Working Families Party, a key progressive group that had endorsed Mr. Sanders in the 2016 race.
Now, their political fortunes have shifted. Mr. Sanders has risen in the polls, while Ms. Warren has plateaued, stymied by a barrage of political attacks that have forced her to make a rare shift in messaging. Leaders for C.P.D. Action, which includes liberal groups focusing on immigration, health care, housing and other issues, said Mr. Sanders had seen a jolt of popularity within the organization in the past two months, surpassing Ms. Warren. This is the first time the group, founded in 2012, has endorsed in the presidential race.
Jennifer Epps-Addison, the group’s co-executive director, called it a “resurgence.”
“What Bernie Sanders has built — it is not arguable,” Ms. Epps-Addison said. “It’s an exciting and different energy than we’ve seen in the Democratic base.”
Mr. Sanders also nabbed the endorsement of the National Nurses United, the country’s biggest nurses’ union, in November.
The fight to become the party’s progressive front-runner is having significant effects on the battle for the Democratic nomination. Former Vice President Joseph R. Biden Jr. continues to lead in polling with the support of nonwhite and working-class voters, while groups like C.P.D. Action and the Working Families Party are seeking to entice these demographics into their progressive coalition. If they are successful, it may upend the primary.
But without a clear candidate atop the progressive coalition, and Mr. Sanders and Ms. Warren still battling for pole position among their ideological base just two months before the Iowa caucus, some worry that the left will miss a critical window to overtake Mr. Biden and define the Democratic Party’s future.
“I’m a little worried about the split,” said Gustavo Torres, president of CASA in Action, a Latino and immigrant organization that is an affiliate of C.P.D.
Maurice Mitchell, the national director of the Working Families Party, acknowledged that the race remains fluid, and the electoral picture on the party’s left, like the presidential race at large, can shift at a moment’s notice.
“Warren and Sanders are both giants of the progressive movement,” Mr. Mitchell said in a statement. “We’re with Warren, but I applaud anyone putting their organizing muscle behind either of them. It’s the only way we’re going to win against the corporate Democrats and beat Donald Trump.”
For C.P.D. Action, the endorsement means it will now marshal its affiliates — more than 600,000 members across the country — to organize voters in support of Mr. Sanders in the primary. Leaders said there will be a particular focus on reaching racial minorities and a grass-roots strategy to bring new voters into the process.
Mr. Sanders, Ms. Warren and the former cabinet secretary Julián Castro were finalists for the group’s endorsements. C.P.D. Action did not release raw vote totals from its affiliates, but the Vermont senator secured a commanding 75 percent of the vote on the second ballot against Ms. Warren, said a person familiar with the process.
The group’s endorsement comes after Mr. Sanders also secured the backing of three of the most prominent and progressive members of the House: Representatives Alexandria Ocasio-Cortez of New York, Rashida Tlaib of Michigan and Ilhan Omar of Minnesota.
Ms. Ocasio-Cortez campaigned for Mr. Sanders in eastern Iowa last month.
“When people try to accuse us of going too far left — we’re not pushing the party left,” Ms. Ocasio-Cortez said during a rally in Coralville. “We are bringing the party home.”
The split among progressive groups shows that while Mr. Sanders and Ms. Warren are often seen as interchangeable left-wingers by the party’s moderates, leading progressives see tangible differences.
Ms. Warren has had more success among college-educated white liberals and prominent liberal activists who backed Hillary Clinton in the last presidential cycle. Mr. Sanders is often preferred by the party’s more ardent activists, who are not scared off by his willingness to buck Democratic traditions.
In their own words, Ms. Warren has defined herself as a capitalist working within the Democratic Party. Mr. Sanders has identified as a Democratic Socialist, and is an independent who has not registered with the Democratic Party during his decades in Congress.
However, leaders from C.P.D. Action said it’s that history of outside advocacy that helped sway their support to Mr. Sanders over rivals such as Ms. Warren and Mr. Castro. They clarified that both still have significant good will among the collection of members, even as their members endorse Mr. Sanders.
“His supporters have found each other collectively, and they’ve found a voice in the movement orientation of Bernie Sanders,” Ms. Epps-Addison said. “That’s the energy we need to defeat Donald Trump.”
Mr. Torres said considering the importance of next year’s election, he wants to support someone who can match the outsider persona of Mr. Trump. In that view, he sees Mr. Sanders’s self-identified socialist label as not an electoral liability but a strength.
“How we see it, Senator Sanders very clearly distinguished himself from President Trump on politics and style and behavior,” he said. And while they approve of Ms. Warren, he believes that in order to win in 2020, “we need the biggest distinction possible.”