A recent USA Today-Suffolk University poll found that about 20 percent of Sanders supporters say they do not intend to vote for Biden. About 60 percent said they are not excited about supporting his nomination. Meanwhile, a Pew Research Center survey found that 47 percent of Sanders supporters said that differences between Biden and Sanders will keep the party from uniting behind the presumptive nominee.

Weaver argued that Sanders’s coalition will play an outsized role in the battleground states that will be critical to winning the 2020 election, such as Wisconsin, Michigan, Pennsylvania, Arizona, Florida, Iowa and North Carolina — all states where the Trump campaign and affiliated outside groups are already spending tens of millions of dollars in advertisements.