Opinion writer
Despite Hillary Clinton's delegate gains on June 7, presidential candidate Bernie Sanders promised to "continue to fight for every vote and every delegate," until the Democratic convention. He also slammed GOP rival Donald Trump as "a candidate whose major theme is bigotry." (Jenny Starrs/The Washington Post)

THE MORNING PLUM:

Hillary Clinton decisively defeated Bernie Sanders in the big delegate-rich states of California and New Jersey, and in a rousing, emotional speech last night, she laid claim to a piece of American history as the first woman ever to be the presumptive nominee of a major party. But Sanders is still digging in, and in his own speech last night, he vowed to fight on to the convention, adding: “the struggle continues.”

In interviews with me, however, two of Sanders’s most important supporters in Congress — Senator Jeff Merkley and Rep. Raul Grijalva, the co-chair of the Congressional Progressive Caucus — said Sanders would have to accept the inevitably of Clinton’s nomination, and begin the process of getting behind her.

“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,” Merkley, who is Sanders’ sole supporter in the Senate, told me. “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.”

Clinton has now won not just a majority of the overall delegates, with super-delegates factored in. She also has easily secured a majority of the pledged delegates, who are allocated proportionally according to the voting in primaries and caucuses. The voting is now all but over, but Sanders is apparently going to continue to try to persuade super-delegates to support him.

The problem for Sanders is that this now requires him to explicitly call on the super-delegates to overturn the will of the voters as expressed in Dem primaries and caucuses. Given that she currently leads among them by 571-48, this would require a massive stampede away from the person who won far more votes.

Merkley — who is a super-delegate himself — said flatly that Sanders should not pursue this course any longer. “The super-delegates are set aside when you make the judgment that you have a majority of the pledged delegates,” Merkley told me. “I would not support a battle that involves trying to flip super-delegates.”

Grijalva, meanwhile, told me that he expected Sanders to continue trying to win over super-delegates, but only for a limited period of time.

“The reality is unattainable at some point. You deal with that. Bernie is going to deal with this much more rapidly than you think,” said Grijalva, who is also a super-delegate. “At some point, when we’re trying to flip 400 super-delegates, 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.”

“He’s gonna do the right thing,” Grijalva said.

On the night six states including California and New Jersey went to the polls, Sen. Bernie Sanders (I-Vt.) vowed to continue "the struggle," even as rival Democratic presidential candidate Hillary Clinton had pivoted to thanking supporters and slamming Republican Donald Trump. (Sarah Parnass/The Washington Post)

Meanwhile, leading liberal groups that have backed Sanders are now in a bind: they are on record opposing the idea that super-delegates should overrule the will of the voters, yet Sanders is now arguing precisely that.

“Democracy for America has said consistently since 2007 that the winner of the majority of the pledged delegates should be the nominee,” said Neil Sroka, a spokesman for Democracy for America, the progressive group founded by Howard Dean, which has backed Sanders. “The system is what it is, and Sanders is within his rights to pursue super-delegates. But at the end of the day, DFA believes that the winner of the majority of the pledged delegates should be the nominee.”

“That’s not going to change, and Senator Sanders fully understands that,” Sroka added.

Another thing that could make this harder for Sanders is that, now that Clinton has officially secured a majority of pledged delegates, he’s putting super-delegates in an awkward position by asking them to back him. That’s because they are being asked to go against the will of the voters. Asked if this could be a problem for super-delegates, Grijalva replied: “You’re right.”

“It becomes not only awkward, but more difficult,” Grilajva said, adding that the argument that we should wait to determine the will of the voters was now gone.

To be sure, none of this means Sanders is not fully within his rights to pursue concessions on process and the at the convention. Both Merkley and Grijalva noted that the Clinton camp and the party should make such concessions in order to facilitate party unity.

“I’m certainly going to be encouraging Secretary Clinton and Senator Sanders to work incredibly hard to bring their teams together,” Merkley said, adding that one way to do this would be to ensure that the convention is seen as a place where agreement is reached on “many of the core issues that Bernie Sanders has raised.”

“As they reach agreement on these things, it will be very important for Senator Sanders to link arms with Secretary Clinton,” Merkley said. “Bernie Sanders has been absolutely clear that he’s going to do everything possible to beat Donald Trump. He also is determined to sustain a movement behind these core issues that have reverberated so powerfully.”

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* HILLARY WINS CALIFORNIA AND NEW JERSEY: Early this morning, the Associated Press called California for Hillary Clinton, giving her a decisive 56-43 victory there. Clinton won New Jersey by 63-37, and also edged Sanders in South Dakota and New Mexico, while Sanders won in Montana and North Dakota.

The upshot here is that Clinton’s pledged delegate lead will expand by a sizable margin.

* OTHER SENATORS WANT SANDERS TO STEP ASIDE: NPR reports that multiple Dem Senators not allied with Sanders are also gearing up to persuade him to stop contesting the nomination. Note this:

How Sanders handles the coming weeks, or months, could directly impact the goodwill — and, therefore, clout — he’ll enjoy in the chamber should he return. At the moment, Democratic leaders are gingerly giving the senator space to figure out his next steps….But other Senate Democrats say the way the Sanders campaign is defiantly carrying on could jeopardize the senator’s influence if he tries to reshape his role in the Senate when he rejoins them.

This is key: If Sanders can convert his movement into greater influence in the Senate, he could perhaps help exert some pressure on a Clinton presidency on his key issues.

* ENTER ELIZABETH WARREN: The Post reports that Democrats are quietly laying the groundwork for a delicate effort to unite the party, and Elizabeth Warren will be pivotal:

Warren…is seen by other leaders of the party as uniquely credible and positioned to play one of the most influential roles in bridging the Clinton and Sanders divide. A Warren adviser, who spoke on the condition of anonymity to speak candidly, said of the senator, “She takes the threat of Trump very seriously and she takes seriously her potential role in helping unify the party.”

Over the weekend, Warren said: “I don’t believe in super-delegates. I don’t think that super-delegates ought to sway the election.”

 * WHAT’S NEXT ON BERNIE’S SCHEDULE: The next days will be critical:

Clinton has said that she will reach out directly to Sanders in the coming days. The senator was scheduled to fly home to Burlington, Vt., on Wednesday and had already planned to be in Washington on Thursday for a rally, five days ahead of the final primary of the year in the nation’s capital.

In Washington, many top Dems will directly make the case to Sanders that he can . Obama and Sanders are set to meet tomorrow, at Sanders’s request.

 * HILLARY CALLS FOR UNITY: An important quote from her victory speech last night:

“Let there be no mistake. Senator Sanders, his campaign, and the vigorous debate that we’ve had about how to raise incomes, reduce inequality, increase upward mobility, have been very good for the Democratic Party and for America. This has been a hard fought, deeply felt campaign. But…we all need to keep working toward a better, fairer, stronger America. Now I know it never feels good to put your heart into a cause or a candidate you believe in and to come up short. I know that feeling well. But as we look ahead to the battle that awaits, let’s remember all that unites us.”

That’s an unequivocal declaration that the Sanders movement was good for the Democratic Party and the country. But still, the hard unifying work lies ahead, and Clinton will have to do a lot of it.

* SANDERS CAMPAIGN LAYS OFF STAFF: The New York Times reports that Sanders is laying off at least half of his campaign staff as it all winds down:

Many of those being laid off are advance staff members who often help with campaign logistics, as well as field staff members who have been working to garner votes for the senator, according to a campaign official and a former campaign staff member, both of whom spoke on condition of anonymity. Some campaign workers may move into jobs at Mr. Sanders’s Senate office, but others will be terminated, they said.

Look for other little stories such as these to continue reinforcing the sense that it’s over.

* AND SANDERS SUPPORTERS WILL TAKE SOME WOOING: CNN reports this telling color from Sanders’s speech in California last night:

Before Sanders arrived a huge video screen towering above the crowd showed California’s early returns — with Sanders losing by a large margin — the crowd shouted “Bulls—t! Bullsh—t.” When the channel flipped to CNN — again showing the evening’s strong results for Clinton — the crowd thundered: “Turn it off! Turn it off!”

This reminds me very much of the atmosphere among Clinton supporters in 2008 — there was widespread disbelief and anger about what was happening among them as Clinton vowed to keep up the fight, but she conceded days later.