Win McNamee/Getty Images Sen. Elizabeth Warren (D-Mass.), left, and Sen. Bernie Sanders (I-Vt.) appear on the debate stage in Charleston, S.C. Some of Warren's liberal supporters are backing Sanders.

The Working Families Party, an influential progressive organization, endorsed Vermont Sen. Bernie Sanders for president on Monday ahead of another round of critical primary contests.

The WFP, a New York-based group with a presence in the general election battleground states of Pennsylvania and Wisconsin, endorsed Sen. Elizabeth Warren (D-Mass.) in September, helping to propel her brief ascent as a front-runner in the field.

Following Warren’s withdrawal on Thursday, Sanders is now the only choice for the organization, according to Maurice Mitchell, the WFP’s national director.

“When we endorsed Elizabeth Warren, we felt it was important to state the obvious: that there were two progressives in the race and it was actually a good thing that there were two bold progressives in the race arguing for structural change of our democracy and our economy,” Mitchell told HuffPost. “And now there’s one progressive in the race. And we are still committed to that change — the change that we felt Elizabeth Warren’s campaign was presenting a unique case for.”

“In a race where the stark contrast couldn’t be clearer between Bernie and [former Vice President Joe] Biden, it’s critical for progressives to stay in the fight,” he added.

Sanders won the WFP’s endorsement in 2016 and was ranked a close runner-up in the endorsement process this cycle, which the WFP has characterized as a “ranked choice” voting system that effectively makes Sanders the group’s pick in light of Warren’s departure. The group’s decision to endorse Warren in September drew a wave of criticism from Sanders supporters who suggested that the weighted votes of key WFP stakeholders, rather than the broader membership, had put Warren over the top.

In his interview with HuffPost, Mitchell made a positive case for Sanders’s candidacy, praising the Vermont senator’s cultivation of a multi-racial, working-class coalition with particular “inroads” in the Latino community.

“A feature of his candidacy is how prescient he’s been and some of the ways he’s been consistent ― on ‘Medicare for All,’ for example,” Mitchell said. “That consistency, along with some of the growth [since 2016], has been noticeable.”

The group’s blessing reflects the consolidation of some of Warren’s more liberal supporters behind Sanders after a disappointing showing on March 3 prompted Warren to call it quits. The Progressive Change Campaign Committee, another liberal Warren backer, also encouraged its members to vote for Sanders, though it framed the recommendation as a tactical choice designed to prolong the competition for progressive votes.

Several former Warren staffers and surrogates have publicly endorsed Sanders as well, but Warren herself has yet to weigh in. Mitchell said the WFP has expressed its views to Warren and her former campaign.

The WFP does not have significant reach in Michigan or any of the other five states where Democrats head to the polls on Tuesday. The group’s endorsement may still help generate momentum for Sanders ahead of Tuesday’s contests.

Sanders is hoping to slow Biden’s rise in Michigan, a state that gave him an upset win at a key moment during his ultimately unsuccessful primary battle with Hillary Clinton 2016. The Vermont senator held five major rallies in Michigan over the weekend, including an event in Grand Rapids on Sunday that featured the famed civil rights leader Rev. Jesse Jackson. Jackson, whom Sanders endorsed for president in 1988, announced that he is backing Sanders’s presidential bid.