With Hillary Clinton assuming the mantle of presumptive Democratic nominee, one question is looming on Tuesday, the last big voting day of the primary season: When will Bernie Sanders drop out?

Clinton and her allies have been careful to not force the issue, with her campaign offering notes of caution Monday night, even as The Associated Press and multiple networks declared that Clinton had amassed enough pledged delegates and superdelegates to clinch the nomination.


It was Clinton, after all, who hung in until the bitter end in 2008 — when, on this exact day eight years ago, she conceded to then Sen. Barack Obama, delivering an eloquent speech about her failure to shatter the “highest, hardest glass ceiling” despite the 18 million cracks that voters made in it.

And on Tuesday morning, her campaign stopped short of declaring victory, and seemed eager to guard against a loss in California, which would still be an embarrassing blow.

"All these races are competitive. You know, we're never exactly sure what's going to happen," said Robby Mook, Clinton's campaign manager, on CNN. "That's why we're sending a clear message to our supporters and our volunteers, stay at this. If you haven't voted yet in California, vote. If you haven't returned your ballot, return it. To all of our volunteers, keep working hard."

He added, “I think we’re going to have a nominee tomorrow."

Bernie Sanders on Monday night was defiant, telling supporters at a rally outside the Los Angeles Memorial Coliseum that there was still hope.

"If we can win, and win big here in California and in the other states, and in Washington D.C., we are going to go into the Democratic convention with enormous momentum," Sanders said. "With your help, I believe, we will come out with the nomination."

Sanders campaign manager Jeff Weaver blasted the media on Tuesday morning for "suppressing voter turnout" by projecting Clinton as the nominee.

Pressed on CNN about the chances of Sanders abandoning his campaign on Wednesday, Weaver responded, "I think there's zero chance of that."

But math is not on Sanders' side.

The hope rests on the idea of flipping enough superdelegates to make up for his deficit of pledged delegates. Sanders headed into Tuesday lagging Clinton 1,521 to 1,812 in pledged delegates, but he is trailing badly among superdelegates, 48 to 571, according to the AP.

That puts Sanders’ overall count at 1,569, and Clinton’s at 2,383 — the magic number needed to clinch the nomination.

Even with the 694 pledged delegates up for grabs in Tuesday’s six contests, Sanders would likely need to convince dozens of superdelegates to switch their allegiance over the coming weeks, an all but impossible task at this point.

And after weeks of defiant predictions of ultimate victory, Sanders on Monday appeared to acknowledge that he would soon have to accept that his wild success this political season had fallen short.

Speaking to reporters at a press conference, he said he would be flying back to Burlington, Vermont on Tuesday night and that he would “assess where we are” with his aides.

There is mounting pressure on Sanders to accept his fate, especially now that Clinton has been deemed the presumptive Democratic nominee.

House Minority Leader Nancy Pelosi, who so far had been reluctant to endorse before the California primary, on Tuesday morning offered her full-throated support for Clinton.

"Well I'm a voter in California and I have voted for Hillary Clinton for president of the United States and proud to endorse her for that position," Pelosi said on ABC's "Good Morning America” on Tuesday morning.

She followed up with a statement that complimented Sanders, who still has a shot of winning her home state of California on Tuesday, even if such a victory would be largely symbolic.

"I congratulate and thank Senator Bernie Sanders for the great invigoration he is bringing to the presidential primary, and welcome the political and intellectual participation of his supporters to advance our shared fight for progress for the American people," she said.

President Obama is also signaling that it’s time for Sanders to step aside so Clinton can focus on what will likely be a brutal general election battle against Donald Trump.

Reports leaked on Monday that Obama had called Sanders on Sunday, and that Obama’s endorsement could come as early as this week.

“He has indicated he wants to spend a lot of time on the campaign trail, so when it’s time to do that, we’ll go out guns ablazing,” said Jennifer Psaki, Obama’s communications director, in an interview with The New York Times. “We are actively thinking through how to use the president on the campaign trail — what works for the nominee, what works for him, and how to utilize his strengths and his appeal.”

Obama, who is enjoying some of the highest favorability numbers of his presidency, is expected to play a pivotal role in the attempts to unify the Democratic Party after a bruising primary season.

Sanders has repeatedly attacked Clinton’s judgment, not only for her vote in favor of the invasion of Iraq in 2002 but also for her use of a private email server during her tenure as secretary of state, which is being investigated by the FBI.

Sanders also has an especially fervent following that may be reluctant to switch allegiances to Clinton, especially if Sanders himself does not make a strong pitch for her.

Minnesota Sen. Amy Klobuchar, a Clinton supporter, said she would like Sanders to decide on his plan of action "as soon as possible."

"Given the kind of strong campaign he has run, the grassroots support he's gotten, this is up to him. But I will say when you look at the numbers here, it's really important to always note that Hillary Clinton is leading with the regular delegates," Klobuchar said on MSNBC. "She is leading significantly with the regular delegates. And so I think that's why it's a really hard argument to make that a bunch of superdelegates should be going against the will of the regular delegates, if in fact after tonight, as we all believe will happen, she will have a significant lead with the regular delegates."

Jeff Merkley, the only senator to have endorsed Sanders, on Tuesday morning was pressed about whether Sanders would follow the usual political playbook and forcefully back Clinton.

He made it clear the Vermont senator is not there yet.

“It’s really a bridge by both sides,” Merkley said on CNN, going on to talk about the need to get rid of superdelegates and have Sanders’ progressive views addressed at the national convention next month “so that people can feel like they’ve been respected and that they’ve been heard.”

But he acknowledged that for the greater good of the party, the time for unification is close.

“We have to be unified to take on Trump. And that unity is going to begin today as soon as the polls close," he said.