Vice President Biden says Bernie Sanders Bernie SandersNYT editorial board remembers Ginsburg: She 'will forever have two legacies' Two GOP governors urge Republicans to hold off on Supreme Court nominee Sanders knocks McConnell: He's going against Ginsburg's 'dying wishes' MORE will endorse his Democratic primary opponent, Hillary Clinton Hillary Diane Rodham ClintonJeff Flake: Republicans 'should hold the same position' on SCOTUS vacancy as 2016 Momentum growing among Republicans for Supreme Court vote before Election Day Warning signs flash for Lindsey Graham in South Carolina MORE.

"I've talked to Bernie, Bernie's going to endorse her, this is going to work out," Biden said in an interview with NPR's "Weekend Edition" to air Sunday. "The Democrats are coalescing even before this occurs."

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Michael Briggs, a Sanders spokesman, would not confirm or deny the vice president's assertion.

“We are in the process of talking” with the Clinton campaign, he said, and noted that the candidates met earlier this month to talk about next steps.

Sanders has been withholding his endorsement for weeks since primary season ended on June 14.

Clinton is seen as the party's likely nominee, having secured enough delegates to win the party's nomination at the July convention.

While Sanders has repeatedly promised he’ll do what he can to stop presumptive GOP nominee Donald Trump Donald John TrumpUS reimposes UN sanctions on Iran amid increasing tensions Jeff Flake: Republicans 'should hold the same position' on SCOTUS vacancy as 2016 Trump supporters chant 'Fill that seat' at North Carolina rally MORE from winning the White House, he's turned down numerous chances to endorse Clinton and has instead shifted his campaign's focus toward winning policy and platform concessions at the convention.

It's not the first time that Biden, who will campaign with Clinton next week in Pennsylvania, got out ahead of the news cycle. His surprise endorsement of same-sex marriage, before President Obama came out in support of the policy, prompted Obama to announce his support soon after.

Biden will hit the campaign trail with Clinton next Friday in Scranton, Pa. He told NPR that vouching for Clinton to voters back home is the best way to support her.

"I understand the hardest thing to do is not writing the check. The hardest thing is vouching. When you vouch for them you say, 'I'm putting my reputation on the line, I believe this person is a good person, has character," Biden said. "You're putting your rep on the line. You're saying, 'I think this person has character,' and that's what I'm prepared to do for Hillary."

In an interview on MSNBC later Thursday evening, Sanders wouldn't confirm or deny Biden's claim. He said he's hopeful he'll be able to give an endorsement but that "we're not there quite yet."

Updated at 9:20 p.m.