WASHINGTON (AFP) - President Barack Obama will play Democratic peace broker on Thursday, hosting defeated and disaffected party ally Bernie Sanders at the White House.
The Vermont senator has refused to acknowledge Hillary Clinton's primary victory, raising the spectre of a split party as it tries to beat Republican nominee Donald Trump in November.
Sanders told his defiant supporters that "the struggle continues," even after crushing defeats on Tuesday to Clinton in California and New Jersey - the two main prizes of the night.
Obama is expected to tread softly - "hearing Sanders out," according to a Democratic source familiar with preparations for the White House meeting - and offering him a very public show of respect for his insurgent campaign.
There is unlikely to be fist-thumping or angry demands for Sanders to face political reality and drop out.
"I think there is a recognition that this is emotionally very challenging," said the Democratic source, who asked not to be named.
"Sanders has poured his energy into this, there is a tremendous amount of pressure. It's like a battleship - it takes a while to change course."
Sanders and Obama have spoken multiple times during the course of the campaign and are said to have a good rapport.
Obama was always going to support Clinton, his former secretary of state, but he has so far refrained from making any formal endorsement.
The outgoing president has lauded Sanders for "energising millions of Americans with his commitment to issues like fighting economic inequality and special interests' influence on our politics."
The stakes are high for Democrats. Decisions now will have an impact on Clinton's chances during the general election in November.
From relative obscurity, Sanders garnered 12 million of the primary campaign's 27 million votes.
He tapped a deep well of anger among young voters who were the lifeblood of Obama's victories in 2008 and 2012.
The risk for Clinton is that Sanders overplays his hand or feels shunned - and continues his insurgency.
"Clinton finds herself in a shaky position she could not have imagined last year," said Larry Sabato, head of the University of Virginia Centre for Politics.
"Weakened by the self-inflicted wounds of her e-mail controversy and her inability to generate enthusiasm in major parts of the Democratic coalition, Clinton has been forced to spend precious time, money, and energy fighting Sanders right to the end."
Some Sanders supporters would indeed like him to battle all the way to the party convention in Philadelphia next month.
For diehard Sandersistas, Clinton - the former first lady, secretary of state and US senator - is the epitome of a political establishment that has failed the people.
More pragmatic supporters are pressing for Sanders to leverage his newfound political clout.
He could still influence the party platform and the next nominating process in 2020.
Actor Mark Ruffalo, a Sanders stalwart, echoed that sentiment, congratulating Clinton on her "historical win."
"My Sanders family, let's keep pushing our Progressive values!" he tweeted.
All eyes will be on Sanders' message at a rally in Washington, also on Thursday.
If there is still no show of unity, all indications are that the next discussion with Obama would be less amiable.