On June 9, President Barack Obama endorsed Hillary Clinton. But at a D.C. rally that same day, Bernie Sanders supporters were on the fence about backing Secretary Clinton in the general election. (Alice Li/The Washington Post)

It had been billed as Bernie Sanders’s big day in Washington. Making a last stand as a Democratic presidential candidate, the senator from Vermont was set to meet with President Obama and other leading Democrats and stage a show of his continuing ability to draw throngs of supporters at an outdoor rally near RFK Stadium.

Only all that was eclipsed — much like his upstart presidential campaign itself — by Hillary Clinton and the muscle of the Democratic establishment.

Shortly after Sanders emerged from his meeting with Obama, word got out that the president was going to trumpet an endorsement of his former secretary of state in a video. And then it became clear that Sen. Elizabeth Warren (D-Mass.), a darling of the political left and Sanders’s ideological soulmate, had also chosen Thursday to throw her support behind Clinton.

The theme of the day soon became Democratic unity, drowning out the conversation about what policy changes and other concessions Sanders might exact in exchange for exiting the race.

Still, the 74-year-old Democratic socialist soldiered on.

After flying down Thursday morning from Burlington, Vt., where he spent the night in his own bed after weeks of campaigning in California, Sanders arrived at the White House about 11 a.m.

Soon afterward, he and the president smiled and chatted as they walked along the White House colonnade, as a throng of White House reporters recorded the moment. They headed into the Oval Office to have their private meeting.

Jane Sanders, the candidate’s wife and a close political adviser, stood behind Sanders as he emerged from the meeting and greeted the press.

Sanders struck a conciliatory note, saying he looked forward to meeting with Clinton “in the near future” to talk about how they can work together to defeat presumptive Republican presidential nominee Donald Trump.

But Sanders also rattled off several of the issues he would like to see incorporated into the Democratic Party platform and become legislative priorities going forward. Among them: fighting childhood poverty, making college more affordable, rebuilding the nation’s “crumbling” infrastructure, and making sure corporate America and the wealthy pay their “fair share” of taxes.

Sanders also made clear that he plans to compete in the final Democratic primary of the campaign season Tuesday in the District. He said he would focus on the issue of D.C. statehood, noting that Vermont has about the same population as Washington but is represented in Congress by two senators and a single House member.

The Clinton campaign released a video on June 9 showing President Obama endorsing her as his successor. (Hillary Clinton)

By the time Sanders arrived on Capitol Hill for a series of afternoon meetings, Clinton’s campaign had released the video of Obama endorsing her, in which he says of Clinton’s pursuit of the presidency : “I don’t think there’s ever been someone so qualified to hold this office.”

After arriving on the Hill, Sanders headed to the suite of Senate Minority Leader Harry M. Reid (D-Nev.).

Sitting on a chair across from Reid by a bookshelf, the Democratic presidential hopeful sat silently as reporters asked him about the six states that voted on Tuesday. Sanders had posted victories in only two.

“Okay you guys, we’re not going to take any questions,” Reid said as Sanders stared straight ahead with his hands on his knees. “That’s kind of the deal that I made.”

Sanders would confer privately with other Senate colleagues before heading to a meeting with Vice President Biden that had been added to his schedule.

The two met at Biden’s residence at the Naval Observatory, said Sanders spokesman Michael Briggs.

“He is seeking out people he admires and respects,” Briggs said of Sanders.

A crowd of thousands of Sanders die-hards started gathering on a field near the stadium hours before he was scheduled to address them sometime after 7 p.m.

Although some expressed a grudging acceptance of Sanders’s fate, others were clearly not ready to start the grieving process.

Marion and Malcolm Fox arrived at the rally from Bowie, Md., more than two hours before the event started.

Marion Fox, a public-school teacher, said she was not giving up on Sanders, despite Obama’s endorsement of Clinton and recent primary results in California and New Jersey.

“I am not giving up hope at all,” she said. “There is still a big margin that will write him, in and that is what we are hoping on. Bernie is the person that we want for president.”

Others in the audience said they weren’t ready for Democratic unity.

Malik Lloyd, 26, an inline skating instructor from Southeast Washington, said he just can’t support Clinton if Sanders is not the nominee.

“I never trusted her from Day One, and I couldn’t stand her husband,” Lloyd said as he waited to get into the rally. “I voted for Barack Obama the first time, but the change I was looking for never happened.”

Robert Costa, Juliet Eilperin and Hamil Harris contributed to this report.