Warren can’t assume that Sanders supporters would move to her and not to Biden. But she is betting that consolidating the left is her best path to victory. The WFP endorsement is a step in that direction, not simply because it will add some field troops to Warren’s side. “What’s most important is that it sets up a permission structure for people to gravitate to the candidate with the most authentic progressive brand,” Kwatra says. “It’s an unequivocal statement that the progressive energy in the race is increasingly moving toward Warren. It’s a pretty emphatic exclamation point in the primary-within-a-primary fight between her and Bernie, and it’s going to allow other progressive organizations and unions to get behind Warren.”

The next front in the battle will be trying to land crucial institutional players in battleground states, like AFSCME and the state teachers union in Iowa and the Culinary Workers union in Nevada. “You could argue that Hillary Clinton wouldn’t have squeezed by us in Iowa in 2016 if she hadn’t had SEIU and AFSCME working as hard as they did,” Longabaugh says. “Clearly they gave her a slight organizational boost.”

The WFP endorsement could also help Warren in her pursuit of the glossiest individual prize on the left: The backing of Ocasio-Cortez. The star congresswoman volunteered on the Sanders campaign in 2016, and traveled to Kansas for a rally with him last year. In March, Ocasio-Cortez met privately with Warren, who later wrote an effusive essay for Time about the freshmen Democratic socialist. This summer both Sanders and Warren endorsed Tiffany Cabán, a progressive outsider running for district attorney in Queens; AOC’s congressional district covers part of the borough. “Bernie is still winning the millennial vote, but Warren is a close second. People’s hearts and minds are split, and I think hers are too,” an Ocasio-Cortez colleague says. “If she ends up staying neutral, it may be more damaging for Bernie—but it would be less damaging to AOC.”