Biden’s biggest problem, Greenberg said, is that the Democratic Party has not unified behind him. In fact, Biden is now behind where Clinton was with Bernie Sanders voters in 2016, with more than 20 percent of the democratic socialist’s backers saying they would not vote for him, even as 87 percent of them pledge to vote for a Democrat for Congress. At a similar point in the 2016 cycle, roughly 15 percent of Sanders voters said they wouldn’t vote for Hillary and Greenberg’s own polling through Democracy Corps around Election Day found the same.

“They lean towards the Democrats, but Biden’s not getting their votes yet,” Greenberg told POLITICO.

Even before Greenberg’s presentation, Biden’s campaign signaled that it recognized he had a serious problem with the left-wing. While most presidential candidates move to the center after capturing the nomination, Biden has tacked left. He recently partnered with Sanders to create “unity” task forces and Biden’s team has spoken of New Deal-level ambitions. On policy, Biden has shifted on some issues such as immigration and college affordability, and in one case reversed himself when he embraced Warren’s bankruptcy plan.