It had been billed as Bernie Sanders' big day in Washington.

Making a last stand as a Democratic presidential candidate, the senator was set to meet President Barack 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 Senator Elizabeth Warren, a darling of the political left and Sanders' ideological soulmate, had also chosen this time 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 from Burlington, Vermont, where he spent the night in his own bed after weeks of campaigning in California, Sanders arrived at the White House about 11am. Soon afterward, he and the President headed into the Oval Office to have their private meeting.

Sanders struck a conciliatory note, saying he looked forward to meeting 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 next Wednesday in the District.

President Barack Obama walks with Democratic presidential candidate Sen. Bernie Sanders down the Colonnade of the White House in Washington. Photo / AP
President Barack Obama walks with Democratic presidential candidate Sen. Bernie Sanders down the Colonnade of the White House in Washington. Photo / AP

By the time Sanders arrived on Capitol Hill for 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 Reid.

Sanders would confer privately with other Senate colleagues before heading to a meeting with Vice-President Joe 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 addressed them. Although some expressed a grudging acceptance of Sanders' fate, others were clearly not ready to start the grieving process. Marion and Malcolm Fox arrived at the rally from Bowie, Maryland, more than two hours before the event started.

Marion Fox, a public-school teacher, said she was not giving up on Sanders,.

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

Malik Lloyd, 26, an inline skating instructor from 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.

"I voted for Barack Obama the first time, but the change I was looking for never happened."

Bernie Sanders, accompanied by his wife Jane Sanders, speak to reporters outside the White House in Washington. Photo / AP
Bernie Sanders, accompanied by his wife Jane Sanders, speak to reporters outside the White House in Washington. Photo / AP

Later Biden and Warren delivered a one-two punch to Donald Trump in speeches that signalled the increasingly co-ordinated effort by Democrats to push the presumptive Republican presidential nominee and his restive GOP allies on Capitol Hill.

Warren adopted the mogul's own mocking tone to call him "thin-skinned, racist bully" and "a guy who inherited a fortune and kept it rolling along by cheating people".

She focused on Trump's recent "race-baiting" of Gonzalo Curiel, a Mexican-American federal judge overseeing a lawsuit against him.

"Donald - what you are doing is a total disgrace," said Warren.

"You should be ashamed of yourself. Ashamed for using the megaphone of a presidential campaign to attack a judge's character and integrity simply because you think you have some God-given right to steal people's money and get away with it. You shame yourself and you shame this great country."

Warren's searing rhetoric, delivered to the largest ballroom in the Capitol Hilton, came just two hours before she told MSNBC's Rachel Maddow that she was endorsing Clinton. Warren, who once signed a letter encouraging Clinton to run for president, was the lone holdout among Democratic women in the Senate to back her. Instead, in recent weeks, she took on the role of leading Trump critic, going round after round with the candidate on his preferred social media platform, Twitter.

That pugilistic approach has increased Democrats' interest in Warren as potential vice-presidential nominee for Clinton.

Bernie Sanders greets supporters after speaking at a rally in Washington. Photo / AP
Bernie Sanders greets supporters after speaking at a rally in Washington. Photo / AP

A leading expert on debt and personal finance, even before her 2012 run for Senate, Warren has vast political clout with many supporters of Sanders. In 2014 and early 2015, before Sanders ran for president, many progressive activists attempted to draft Warren herself into the race.

Biden criticised the Republican majority's decision to refuse to hold hearings for Obama's selection for the Supreme Court, Merrick Garland - "a judge of unquestionable credentials"- until the next president takes office, asking how they consider giving that duty to Trump.

"I don't think the framers envisioned a candidate accusing a federal judge being incapable of reaching a fair decision because of his ethnic descent," said Biden. "It's my view that when a presidential candidate attacks a federal judge, he cannot be trusted to respect the independence of the judiciary as president."

Their speeches demonstrated that Biden and Warren plan to play aggressive roles as political pitbulls going after Trump and linking him to congressional Republicans.

"Trump isn't a different kind of candidate: He's a Mitch McConnell kind of candidate," said Warren.

"Paul Ryan and Mitch McConnell want Donald Trump to appoint the next generation of judges. They want those judges to tilt the law to favour big business and billionaires like Trump. They just want Donald to quit being so vulgar and obvious about it."

Having Biden and Warren in her corner gives Clinton a major boost, both in terms of surrogates on the campaign trail and in terms of symbolic unity for Democrats. Both are now in Clinton's camp, and trying to coax voters who drifted from the presumptive nominee as the primaries dragged on.

"I love her," said Peter Dotson, a law student from Minneapolis, of Warren.

"I wish she'd have run for president. I'm glad Bernie ran, but he was never electable - and Warren could have won."