“The data shows voters pretty clearly that if you don't want Joe Biden as the nominee, the best chance we have to prevent that is this contest boiling down to Warren and Biden,” said Adam Green, co-founder of the Warren-aligned Progressive Change Campaign Committee. “She can unite and energize the party and is the best foot forward for progressives to get past Biden and Trump.”

In the closing weeks of the campaign, Warren has sought to position herself as a unity candidate who can bring together the moderate and liberal wings of the Democratic Party. But progressive leaders and organizations have increasingly consolidated behind Sanders, who has risen in early-state and national polling. He is first in Iowa and New Hampshire, according to the RealClearPolitics polling average.

The question of how to best defeat Biden has been a source of anxiety among left-wing activists, with some worrying that Sanders and Warren could split the vote and hand the nomination to him. Other progressives have argued that Sanders and Warren should both stay in the primary and potentially combine delegates to beat Biden.

The Data for Progress poll showed that if it were three-way race, 42 percent said they would vote for Biden, 30 percent would back Warren, and 23 percent would support Sanders. The rest of the Democratic field was not tested.

The Sanders campaign did not provide comment for the story.

The Data for Progress poll sampled 1,619 registered voters online from January 18 to 26, and the margin of error is plus or minus 2.6 percentage points. Data for Progress, a progressive think tank, has worked with Warren and Sanders’ teams.

