The Sunrise Movement, the collection of young climate activists who have roiled Capitol Hill and the Democratic presidential primary, will announce on Thursday that it is endorsing Senator Bernie Sanders of Vermont, in another sign that left-wing advocacy groups have increasingly coalesced around his candidacy.
In a landslide vote — more than 75 percent of respondents — Mr. Sanders earned the backing of members of the group, which has quickly become politically influential since its founding in 2017.
Once a fledgling collection of college students, frustrated that Democrats and Republicans were not acting more quickly to curb climate change, Sunrise has grown to 318 chapters nationwide, with more than 10,000 members.
Sunrise will host an event on Jan. 12 with Mr. Sanders in Iowa City to formally announce the endorsement. “We believe a Bernie Sanders presidency would provide the best political terrain in which to engage in and ultimately win that struggle for the world we deserve,” Varshini Prakash, a founder and the executive director of the movement, said in a statement. “Senator Sanders has made it clear throughout his political career and in this campaign that he grasps the scale of the climate crisis, the urgency with which we must act to address it, and the opportunity we have in coming together to do so.”
The move represents another step into electoral politics for the group of young activists. After the 2018 midterm elections, the group made national headlines by staging a protest in the office of the incoming House speaker, Nancy Pelosi.
Sunrise’s signature policy, the ambitious proposal known as the Green New Deal, became a crucial litmus test splitting moderates and liberals on climate change, embraced by top-tier candidates like Mr. Sanders, Senator Elizabeth Warren of Massachusetts and former Mayor Pete Buttigieg of South Bend, Ind. Even moderate candidates like former Vice President Joseph R. Biden Jr., the race’s current front-runner, have cited the policy as an inspiration and said its goal of drastically reducing greenhouse gas emissions while also addressing economic inequality was an important framework.
The group’s announcement is one of the last presidential endorsements to arrive from major progressive groups, almost all of which have backed Mr. Sanders. His candidacy in 2016 helped develop much of the left-wing political infrastructure in the Democratic Party — and had huge support among young Democrats in particular — but when the 2020 campaign cycle began, it was not inevitable that he would retain that support.
Young Democratic voters had a bevy of options, including fresh faces like Mr. Buttigieg, former Representative Beto O’Rourke of Texas and Senator Kamala Harris of California. In Ms. Warren, there was another candidate with progressive bona fides — who would also be the first woman in the Oval Office if elected.
In September, the Working Families Party endorsed Ms. Warren over Mr. Sanders, saying that she was better positioned to create a cross-ideological coalition around liberal values and that grass-roots groups needed to choose a side in the primary.
Over the next several months, however, and after Ms. Warren drew significant criticism for a health care proposal that stepped away from an immediate push for “Medicare for all,” the energy on the Democrats’ left flank began to move away from her.
In October, Mr. Sanders announced endorsements from popular House Democrats including Ilhan Omar of Minnesota and Alexandria Ocasio-Cortez of New York, who is a sponsor of the Green New Deal legislation. He has also gained the backing of labor organizations such as National Nurses United, and left-wing advocacy groups including the Center for Popular Democracy Action and People’s Action.
This week, Mr. Sanders was endorsed by Dream Defenders, a Florida-based collection of activists that focuses on criminal justice reform.
Sunrise gave its members two choices — whether to back any presidential candidate at all, and if so, which one. More than 80 percent wanted to support a candidate. About 20 percent chose Ms. Warren.
Some of Sunrise’s leaders said Mr. Sanders’s stature rose among its members in that same period after September. In August, he released a $16.3 trillion plan for a Green New Deal that called for the United States to eliminate fossil fuel use by 2050.
Evan Weber, the political director for the Sunrise Movement, said the group’s advocacy would continue no matter who is the nominee.
“Should Senator Sanders become the next president of the United States, we will push to ensure that he make delivering upon the promise of his Green New Deal platform the top priority of his administration,” he said. “If Senator Sanders does not win the nomination, the stakes of the climate crisis also demand that we can’t sit this election out.”