Sunrise Movement, the influential Green New Deal campaigners, endorsed Sen. Bernie Sanders (I-Vt.) for president on Thursday, boosting the progressive’s credentials as the 2020 race’s leading candidate on climate change.

The endorsement followed a vote among Sunrise Movement’s rank-and-file about whether to back an individual candidate, and then another on whom to support. After six weeks of deliberation, the organization voted by 76% to back Sanders.

“We know that no matter who the next President is, we will need to turn millions of people into the streets and disrupt business as usual in order to win a Green New Deal,” Sunrise Movement’s executive director, Varshini Prakash, and political director, Evan Weber, wrote in an email to supporters Thursday morning. “But our movement has spoken clearly.”

Sanders was the obvious favorite for the group’s endorsement. Sunrise Movement, founded in 2017, is among the many progressive newcomers that cropped up in the wake of Sanders’ unsuccessful but historic 2016 presidential campaign. The nonprofit’s base is dominated by teenagers and 20-somethings who overwhelmingly support the Vermont senator, who has made an uber-ambitious, $16.3 trillion Green New Deal a central plank of his 2020 campaign.

Yet the outcome of Sunrise Movement’s vote is a stinging loss for progressive rival Sen. Elizabeth Warren (D-Mass.), whose proposals for an ocean-focused “Blue New Deal” and endorsements from key figures in the Green New Deal movement place her close behind Sanders in green groups’ ranking of climate plans.

Sanders has already received strong backing from climate advocates. The U.S. Youth Climate Strike endorsed Sanders last month. Reps. Alexandria Ocasio-Cortez (D-N.Y.) and Ilhan Omar (D-Minn.), who both sponsored some of the first pieces of Green New Deal legislation last year, backed Sanders.

Explicitly backing Sanders, however, could undermine Sunrise Movement’s sway over the Democratic nominee if he doesn’t win, said Julian Brave NoiseCat, a Green New Deal policy expert at the unaligned, left-leaning think tank Data for Progress.

“There’s a risk inherent in endorsing anybody,” NoiseCat said Wednesday ahead of the announcement. “Regardless of who comes out ahead at the end of the primary season, we’re going to have to fight like hell to get something done on climate change.”

This was updated to include a statement from Sunrise Movement.