The first endorsement seemed fairly random, and it drew only minor attention. In early September, Elizabeth Warren, a U.S. senator from Massachusetts, announced that she was backing Kendra Brooks, who is running for an at-large seat on Philadelphia’s city council in this November’s election. The second endorsement, one week later, sparked national headlines and could prove a major boost to Warren’s pursuit of the 2020 Democratic presidential nomination. The connective tissue? Brooks is running for the Philly council on the Working Families Party line, and Warren now has the WFP’s backing for her White House run.

There was no direct quid pro quo driving the two endorsements. But there is a strategic link, one that extends to Warren’s endorsements of Marie Newman, in Illinois, and Jessica Cisneros, in Texas, who are challenging moderate incumbent Democratic congressmen. Warren is methodically trying to become the consensus candidate of the left, undercutting Bernie Sanders (who is also backing Newman) and unifying progressive support against Joe Biden. “Warren getting behind Brooks in Philadelphia was a very smart move,” says Rebecca Katz, a progressive political consultant who is not aligned with any of the Democratic contenders. “If I’m a WFP member, that show of solidarity—right as the WFP is deciding its presidential endorsement—is a good thing for Warren.”

There is some murkiness about just how the WFP awarded Warren its backing—the party’s process involves a weighted vote split between the rank and file and leadership, and some analysts believe the WFP membership went for Sanders, with the party’s bosses throwing decisive support behind Warren. The WFP hasn’t released the specific tally. Regardless, its official backing went to Warren, and it adds to her momentum. “It isn’t determinative,” says Mark Longabaugh, a top strategist for Sanders in 2016. “But it’s an important indicator that Warren’s campaign is doing the blocking and tackling it takes to get the nomination.”

The left is hardly monolithic, yet it is a greater force in this cycle thanks to the larger Democratic field, the galvanizing effect of President Donald Trump, and to Sanders’s success in remaking the policy conversation. “The biggest difference from four years ago is that the left won the debate after 2016,” says Waleed Shahid, who supported Sanders then, helped steer the upset win by Alexandria Ocasio-Cortez in 2018, and is now the communications director for Justice Democrats, the influential liberal advocacy group. “So everyone who is running for president in 2020 is basically running to the left of Hillary Clinton. Even Michael Bennet, one of the most conservative Democratic senators, supports the health care public option.” That policy shift—accelerated by Trump’s retrograde moves on immigration, abortion, and civil rights—is propelling the chase for left-of-center primary voters.

“The left for the Democrats is now what the evangelicals were for the Republicans 20 or 30 years ago—the energy of the party, the fighting spirit of the party,” says Neal Kwatra, a Democratic strategist who has extensive experience with grassroots groups and labor unions. “And do the math: The progressives in this race, collectively, are beating Biden in the polls by two to one.”

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.”