Barack Obama hopes to unite Democrats for the general election

President Barack Obama opened a determined fence-mending mission Wednesday, hoping to use his popularity among Democrats to unite the party behind Hillary Clinton and draw in Bernie Sanders supporters reluctant to give up after a grueling primary fight.

In his first public remarks on the primary since Clinton clinched the nomination, Obama acknowledged the lingering bruised feelings and sought to shower praise on both candidates. He skirted a formal endorsement or a call on Sanders to drop out even as he spoke of the Vermont senator's campaign in the past tense.

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"It was a healthy thing for the Democratic Party to have a contested primary. And I thought Bernie Sanders brought enormous energy and his new ideas and he pushed the party and challenged them. I thought it made Hillary a better candidate," Obama said during a taping of NBC's "Tonight Show." "My hope is that over the next couple of weeks we're able to pull things together. "

Later, Obama made a delicate reference to the party's awkward transition period as he talked up donors at a top-dollar fundraiser. Obama noted Democrats had "just ended or sort of ended our primary season" and declared he was "not too worried" about bringing the party together.

Obama said he was more concerned about overconfidence and Democrats not "doing the hard nuts-and-bolts work" of getting young people and low-income people out to vote.

"We've got to get busy," he said. "We've got to work."

Obama's impending endorsement for Clinton seemed like a fait accompli. Though the White House kept mum about the timing, all signs pointed to Obama endorsing Clinton on Thursday after the president meets with Sanders in the Oval Office.

Democratic leaders hoped the meeting, requested by Sanders, would be a moment of catharsis for the party, sending a signal that even Sanders understands the importance of electing a Democrat in November.

'Give him time': Biden on Sanders

Yet it was unclear whether Sanders was ready to follow that script. The Vermont senator emailed supporters saying "The struggle continues" and vowing to compete in the season's final primary contest next week in the District of Columbia.

"Oh, let him make that decision," said Vice President Joe Biden, urging those calling for Sanders' withdrawal to "give him time." Biden was arranging calls with both Sanders and Clinton to discuss the race before making a public endorsement of his own.

For the president, who reportedly has been itching to get off the sidelines in the race, the key question is whether voters who helped elect him twice will follow his lead now that he's not on the ballot.

There was little reason for overconfidence among Democrats, who haven't seen that powerful coalition of minorities, young people and women reliably show up for candidates not named Obama during the last two midterm elections.

Obama levels of support and turnout among those groups especially African-Americans and Hispanics would make Trump's path to victory exceedingly narrow.

But the yearlong battle between Clinton and Sanders exposed clear rifts: Young people and the most liberal voters fell overwhelmingly in Sanders' camp, while Clinton locked in support among Hispanics and African-Americans.

Obama "will be one of the politicians who can help bring the party together by making the progressive case for Hillary Clinton," said former Obama adviser Dan Pfeiffer, who added that the president's most important job in the campaign would be "turning out his voters in November."

Trump, meanwhile, was making a fresh pitch to Sanders voters, refusing to concede that the Vermont senator's backers were unlikely to vote for him.

In New York, Obama was raising money for Democrats and reaching out to young voters, taping an appearance on the late show hosted by Jimmy Fallon, who's very popular with that key voting group. Obama "slow jammed" the news, reprising one of Fallon's more popular bits. NBC released an excerpt of the interview, but the full interview will not run until Thursday.

White House spokesman Josh Earnest said Obama has deliberately kept in close touch with his supporters even after his last election in 2012 and would be a "particularly influential advocate" for the Democratic nominee.

"I would think that would have some influence on those who supported Sen. Sanders in the primary," he said, "but I also suspect that Sen. Sanders is going to have something to say about this as well."

For months, Obama has been on the sidelines of the Clinton-Sanders showdown, arguing he didn't want to tip the scales before voters weighed in. As an added benefit, his publicly neutral stance may have helped him retain credibility he'll now need to persuade Sanders' supporters who are deeply skeptical of the Democratic establishment's influence in picking the nominee.

In addition to campaign events, Obama is likely to keep up his social media profile and capitalize on his skill with pop culture interviews and the humour-laced digs at Trump, as he's demonstrated in recent speeches.