Democratic presidential candidate Senator Bernie Sanders campaigns in the Silverlake neighborhood on June 7, 2016 in Los Angeles, Calif.
Photo by Scott Olson/Getty

Can Bernie Sanders rally his supporters behind Hillary Clinton once his campaign ends?

Updated

President Barack Obama is now with Hillary Clinton. Sen. Elizabeth Warren is, too. And, eventually, Sen. Bernie Sanders will be with her as well, Democrats expect.

But not even that trinity of progressive politicians could get Scott Ruppel, a 33-year-old engineer at the Department of Defense, to vote for Clinton in November. “I respect their opinion and respectfully decline,” he said. “I’ll probably write in Sanders’ name in November.”

On a day that saw the Democratic Party take major strides toward unifying behind Clinton for the general election, many of Sanders supporters at what could be one of his final rallies said they’re not ready to concede.

Ahead of the District of Columbia primary Tuesday, Sanders gave an hour-long stump speech at a rally in Washington, D.C., that made no mention of Clinton or contesting the Democratic National Convention. The mood was notably somber as many said they were still coming to terms with the events of the week.

RELATED: Elizabeth Warren endorses Hillary Clinton on Rachel Maddow Show

Earlier in the day, Obama welcomed the Vermont senator to the White House with a walk down the West Wing colonnade, a gesture of respect often reserved for world leaders. And Sanders followed his presidential summit with meetings with Senate Minority Leader Harry Reid and Vice President Joe Biden.

Sanders was even sanguine, aides say, when news broke that Obama backed Clinton in a video released Thursday afternoon. Sanders had been given a heads-up and took it in stride. So, too, was he warned that Warren would endorse Clinton on MSNBC with Rachel Maddow.

But even if Sanders seems ready to come in from the cold, it will take work to bring his supporters with him.

Eric Rekstein, a “30-something” gardener, said he came to Sanders’ rally to try to convince the candidate to run as an independent or on a third party. Green Party candidate Jill Stein had just offered Sanders a slot on her party’s ticket.

“I want Bernie to run in November and win. I don’t care about anything else,” said Rekstein.

Mayshaim Tahir, a 26-year-old who works on Capitol Hill, said she would have to think long and hard if Sanders asked her to back Clinton. “I feel like Obama wanted to endorse Bernie, but he’s so entrenched in the political system now, he has no spine,” she said.

Citing her Pakistani-Muslim heritage, Tahir said Clinton is far too interventionist for her. Asked about Trump’s anti-Muslim comments, Tahir said, “Hillary Clinton and Donald Trump are the same to me.”

Usman Ishaq, a high school senior set to graduate in a few days, said Sanders should fight on. “I don’t think this race is over,” said Ishaq. “I hope a miracle can happen and we can have him as president.”

Still, Ishaq said he would vote for Clinton in the fall. “The main goal is keep Donald Trump as far away from a position of power as possible,” he said.

But his friend Alex Patton said Clinton will have to do more to win him over.

RELATED: President Barack Obama formally backs Hillary Clinton

Sanders aides acknowledge there’s a group of dead-enders – the so-called Bernie or Bust movement – whom they can’t control, no matter what Sanders asks them to do.

For instance, Sanders supporters have independently pulled permits from the city of Philadelphia to hold rallies at the Democratic National Convention without the campaign’s consent or involvement.

“We can guarantee you there will be a political revolution,” activist Bill Taylor, who holds three of the five city-issued demonstration permits for the convention, told the Philadelphia Inquirer.

But allies say they’re confident Sanders can bring the vast majority of supporters with him.

“People like me who have been in from the beginning and thousands of others will do what Bernie Sanders believes is the best thing,” said Jonathan Tasini, an activist and Sanders surrogate who challenged then-Sen. Clinton in a primary campaign. “And I think I represent in that statement 90 percent and higher in this movement.”

Clinton can help the process by sticking to the progressive policies she championed in the primary, said Neil Sroka of the pro-Sanders group Democracy for America.

“The question for me is not necessarily whether or not Bernie Sanders supporters will reject Turmp, but how excited they will be to work on a campaign to focus on defeating Donald Trump,” he said.

Iliana Jaime, a high school senior in D.C. who identifies as a socialist, thinks Clinton is motivated more by corporate interests than altruistic ones. But Jaime will back Clinton “100 percent” in November and thinks refusing to vote for the former secretary of state because she’s not perfect is a form of white privilege.

“It’s people who can afford to deal with the consequences of a Trump presidency,” she said. “There’s a lot of moral narcissism going in the Bernie or Bust movement.”

“My personal feelings are far less important than what a Trump presidency means,” she added.

Bernie Sanders and Hillary Clinton

Can Bernie Sanders rally his supporters behind Hillary Clinton once his campaign ends?

Updated