WASHINGTON – Bernie Sanders may have endorsed Joe Biden, but almost a quarter of the Vermont senator’s supporters aren’t jumping on board just yet, according to a new poll.

Nearly 1 in 4 Sanders supporters (22%) said they would vote for a third party candidate, vote for President Donald Trump, not vote in November or were undecided about who to vote for, according to a USA TODAY/Suffolk Poll. When broken down, 2% said they would vote for Trump, 8% said they would vote for a third party candidate, 2% said they would skip voting and 8% are still undecided.

However, the vast majority of Sanders supporters (77%) said they will vote for Biden in the general election in November.

Biden is the presumptive Democratic nominee after Sanders suspended his campaign in early April. Less than a week after dropping out, Sanders, a self-described Democratic socialist, went on to endorse Biden, who is a more moderate Democrat. The Vermont senator has since been emphatic about his supporters backing Biden, and he is working with the former vice president’s campaign via several policy working groups related to more progressive stances.

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“I believe that it’s irresponsible for anybody to say, ‘Well, I disagree with Joe Biden – I disagree with Joe Biden! – and therefore I’m not going to be involved,’” Sanders said in a recent interview with The Associated Press.

Despite Biden and Sanders working together to win over the Vermont senator’s supporters, the majority of them are not enthused by Biden.

A combined 60% of Sanders supporters are not very or not excited at all for Biden’s impending nomination, according to the poll, while a combined 38% said they were very or somewhat excited.

“This potentially impacts not only fundraising and volunteer support, but the all-important “ground game” necessary to win in November – even a digital ground game in the shadow of the novel coronavirus,” David Paleologos, director of Suffolk University Political Research Center, said in a statement.

Paleologos noted that Biden is likely struggling to win over Sanders voters because of disagreements on priorities for the general election. While 57% of Sanders supporters said defeating Trump is more important than standing up for policy proposals like Medicare for All and the Green New Deal, about one-third (34%) said standing up for policy proposals was more important than beating Trump.

David Barker, director of the Center for Congressional and Presidential Studies at American University, said that it's common to see a large percentage of disgruntled supporters from other primary challengers at this point of the electoral cycle.

Barker noted that as late as August 2008, many Hillary Clinton supporters were still expressing that they wouldn't vote for Barack Obama, and there was a similar situation with "never Trump" voters in 2016.

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"In the end, though, most voters tend to come around because the dynamics of the campaign tend to 'bring people home,'" Barker said.

However, Barker said that 2016 was a contradiction to this rule among Democrats, adding that "we can’t be too sure that they won’t do the same thing in 2020."

But unlike Clinton, Barker said, Biden is less of a polarizing figure and is making more overtures with progressive voters than Clinton did in 2016.

"The loathing that many on the left had for (Clinton) is hard to understate, and it is not matched by their lack of enthusiasm for Biden," Barker said. "They may not love him, but they do not loathe him ... in the same way they did Clinton."

The survey was conducted from April 18 to 25, with 638 Sanders voters contacted by mobile and landline phone. There was a margin of error of plus or minus 4 percentage points.