Pro-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 lawmakers are encouraging the Vermont senator to exit the race for the Democratic nomination so the party can unify behind 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, the presumptive nominee.

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“Once a candidate has won a majority of the pledged delegates and a majority of the popular vote, which Secretary Clinton has now done, we have our nominee,” Sen. Jeff Merkley Jeffrey (Jeff) Alan MerkleyThe Hill's Morning Report - Sponsored by The Air Line Pilots Association - Trump, Biden renew push for Latino support Sunday shows - Trump team defends coronavirus response Oregon senator says Trump's blame on 'forest management' for wildfires is 'just a big and devastating lie' MORE (D-Ore.), the first senator to back Sanders's presidential campaign, told Greg Sargent at The Washington Post's Plum Line on Tuesday.

“This is the moment when we need to start bringing parts of the party together so they can go into the convention with locked arms and go out of the convention unified into the general election," Merkley said to The Washington Post.

Clinton won four of six state contests on Tuesday, a day after The Associated Press said she had won the 2,383 delegates needed to clinch the nomination.

Sanders has argued that Clinton can only surpass that threshold with the support of superdelegates, the unbound party officials who don't cast votes until the Democratic National Convention.

Yet Clinton's large lead in the popular vote and in pledged delegates means few superdelegates are likely to switch their allegiance to Sanders.

Merkley, a superdelegate, said Sanders shouldn't even try to flip superdelegates.

“The superdelegates are set aside when you make the judgment that you have a majority of the pledged delegates,” Merkley said. “I would not support a battle that involves trying to flip superdelegates.”

Rep. Raul Grijalva (D-Ariz.), another Sanders supporter and superdelegate, said Sanders will eventually "do the right thing."

“At some point, when we’re trying to flip 400 superdelegates, and it’s not gaining traction, I think you have to come to the conclusion that it’s not going to happen. You just move into a different direction. And that different direction is that we begin to try to integrate the party.”

Clinton declared herself the party's nominee after several primary wins Tuesday night, but Sanders vowed Wednesday morning to carry the fight to the party's convention in July.

Now his top supporters in Congress are urging Sanders to accept Clinton's nomination and begin the process of getting behind her to defeat presumptive Republican 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 in November.