Bernie Sanders has promised to work with Hillary Clinton to defeat Donald Trump in the 8 November US presidential election, but hasn't formally pulled out of the race for the White House.
Mr Sanders said in an online speech to supporters today he did not endorse Mrs Clinton, but made it clear he was shifting his focus to building a grassroots movement to fight for his liberal policy agenda and transform the Democratic Party.
"The major political task that we face in the next five months is to make certain that [Republican presumptive nominee] Donald Trump is defeated and defeated badly, and I personally intend to begin my role in that process in a very short period of time," the Vermont senator said.
"I also look forward to working with Secretary Clinton to transform the Democratic Party so that it becomes a party of working people and young people, and not just wealthy campaign contributors," he said.
Mr Sanders, who has resisted pressure from Democrats to exit the White House race and back Mrs Clinton after she clinched the party nomination last week, said he would keep fighting for his goals of reducing income inequality, removing big money from politics and reining in Wall Street.
"Defeating Donald Trump cannot be our only goal. We must continue our grassroots efforts to create the America that we know we can become," he said.
"And we must take that energy into the Democratic National Convention on July 25 in Philadelphia where we will have more than 1900 delegates."
Sanders has kept his campaign alive as leverage to force concessions from Mrs Clinton on his policy goals during deliberations on the party's issues platform, and on the reforms he seeks in the Democratic Party's nominating process.
But he has laid off some staff, stopped campaigning and dropped plans to court unbound delegates in an unspoken acknowledgement the former secretary of state would be the nominee.
Mr Sanders met with Mrs Clinton on Tuesday night after the nominating process ended, and said he would continue his discussions with her campaign to make certain "the Democratic Party passes the most progressive platform in its history, and that Democrats actually fight for that agenda".
"Our vision for the future of this country is not some kind of fringe idea. It is not a radical idea. It is mainstream. It is what millions of Americans believe in and want to see happen," Mr Sanders said.