With Hillary Clinton securing the delegates needed for the Democratic nomination, Sen. Bernie Sanders is facing increased pressure to drop out of the race and unite the Democratic party.
His fellow senators, while giving him time to consider options, say they are confident the Vermont senator will "do the right thing."
"I think Sanders will be on board, and I think that he will be vigorous in his support of Hillary," said Sen. Sherrod Brown, an Ohio Democrat, who was pushing a progressive tax policy agenda Tuesday at the Center for American Progress Action Fund. "I don't know when that starts."
Sen. Tim Kaine, D-Va., who like Brown has been touted as a potential Clinton vice presidential pick, said he expected Senate Democrats would be reaching out to Sanders, encouraging him to unify the party.
"I have confidence that once the dust settles tomorrow and she's cleared this margin, that he's going to make the pivot to help us unify the party," Kaine said in a brief interview Tuesday morning.
"I have the confidence because Donald Trump is contrary every value [Sanders] has ever expressed," Kaine added. "And Bernie is a very sincere person. And if he is as sincere as i believe him to be, and he is, he will realize that this is an existential threat to the country, and he'll want to unify us all."
Sanders vowed to continue fighting until the Democratic National Convention in late July, hoping to convince the party's most loyal delegates that he is the best candidate to face Trump, the presumptive GOP nominee.
Sanders says the math is inaccurate, as the delegate trackers incorporate super delegates — or party officials and elected leaders who have a vote at the convention and are not bounded to a single candidate — who don't vote until the convention. So, the campaign intends to court super delegates, who now support Clinton 571 to 48. About 100 are still undecided.
Sen. Amy Klobuchar, D-Minn., pointed out that Clinton also leads in the popular vote and the regular or pledged delegate count. "It's a really hard argument to make that a bunch of super delegates should be going against the will of the regular delegates," she said in an interview with MSNBC.
Clinton reminded reporters on Monday that super delegates played a role in her loss to Barack Obama in 2008. “Tomorrow is eight years to the day after I withdrew and endorsed then-Senator Obama,” she said. “I believed it was the right thing to do.” That year, she conceded four days after the AP called the race for Obama.
Clinton and Sanders are competing Tuesday in six states: California, New Jersey, New Mexico, Montana and South Dakota have primaries and North Dakota is holding caucuses.
Some Democrats say Sanders should remain in the race until the primary process ends next week with balloting in the District of Columbia.
"We’ve said all along, I don’t think anybody should tell him when to bow out until the primaries are all over," Sen. Claire McCaskill, D-Mo., said Monday, before news broke that Clinton had the delegates. "And when the primaries are all over, I hope he will respect the math.”
"Timing isn't quite as important to me as his sticking to his word," Klobuchar said Tuesday. "He's made it clear that one, he will support our nominee. And two, that he will do everything it takes to defeat Donald Trump."
But others have been more vocal that Sanders should step aside.
"Absolutely, yes, I think so," Sen. Dianne Feinstein, D-Calif., said Monday.
"And I believe she will win California and she will win the delegate votes," said Feinstein, a Clinton supporter. "So let’s sit down and talk about how we can unite the party. That’s what needs to be done. ... And it should be sooner rather than later."
Conversations about the changing the Democratic primary rules and influencing the party platform are some of the most talked-about avenues to bring the Sanders campaign into the fold
"After this cycle is over, there are going to be a whole host of reforms debated," said Clinton supporter Sen. Ron Wyden, D-Ore. "No question about that. I think that’s something all sides agree on.”
Wyden's fellow Oregon Democrat, Sen. Jeff Merkley, is Sanders' lone Senate endorsement. Merkley's spokeswoman did not respond to a request for comment.
But in late May, Merkley said he was focused on party unity in response to a question about whether he was reaching out to fellow senators about supporting Sanders' campaign.
"There are really three legs to that stool. One is the Democratic National Committee, one is the Clinton team and one is the Sanders team," Merkley said.
Merkley also said he was "very heartened" by the DNC's decision to allow Sanders to name five of the 15-member convention drafting committee.
While the Sanders campaign vows to keep moving forward, the Clinton campaign treated Tuesday's primaries as the effective end of the nominating contest.
Clinton supporters gathered in battleground states Tuesday evening for watch parties for the former secretary of State's speech. There will be nearly a dozen states holding such gatherings, a campaign official said.
Niels Lesniewski and Eric Garcia contributed to this report .