US President Barack Obama has endorsed Hillary Clinton to be his successor.
The move came after Obama met with her rival, Senator Bernie Sanders who has said he would work with Clinton to stop the Republican's presumptive nominee Donald Trump.
In his endorsement, Obama said: "I don't think there's ever been someone so qualified to hold this office."
Obama praised his former secretary of state's experience and grit, and urged Democrats to unite behind her in the fight against the Republicans in the autumn.
"Look, I know how hard this job can be. That's why I know Hillary will be so good at it," Obama said in a web video circulated by the Clinton campaign. "I have seen her judgment. I have seen her toughness."
Obama called for unity among Democrats and vowed to be an active force on the campaign trail.
As the video circulated, Clinton's campaign announced their first joint appearance on the campaign trail will be on Wednesday in Green Bay, Wisconsin. The campaign said Obama and Clinton will discuss building on the progress made during his presidency "and their vision for an America that is stronger together".
Obama's endorsement came as the Democratic establishment piled pressure on Clinton's primary rival, Sanders, to step aside so Democrats could focus on defeating Trump.
Sanders emerged from his meeting with Obama and inched closer in that direction. Although he stopped short of endorsing Clinton, the Vermont senator told reporters he planned to press for his agenda at the party's July convention and would work with Clinton to defeat Trump.
"Needless to say, I am going to do everything in my power and I will work as hard as I can to make sure that Donald Trump does not become president of the United States," he said.
Sanders, standing in the White House driveway with his wife, Jane, at his side, said he would compete in the Washington DC primary on Tuesday, the party's final contest, but noted his interest was largely in pushing for statehood.