President Barack Obama formally endorsed Hillary Clinton to succeed him as president of the United States last night (Thursday), calling her the most qualified person ever for the job.
For months Mr Obama had remained neutral as Mrs Clinton and Bernie Sanders, the socialist senator from Vermont, competed for the Democratic Party's nomination.
In a three-minute video Mr Obama said: "I want to congratulate Hillary Clinton on making history. I know how hard this job can be, that's why I know Hillary will be so good at it.
"In fact, I don't think there's ever been someone so qualified to hold this office. She's got the courage, the compassion, and the heart to get the job done. I have seen her judgment, I have seen her toughness up close."
Mr Obama said it was a "testament to her character" that Mrs Clinton had agreed to be his secretary of state after their own hard-fought contest for the presidential nomination in 2008.
He added: "I'm with her. I am fired up, and I cannot wait to get out there and campaign for Hillary."
White House sources said Mr Obama had been keen for some time to get out on the campaign trail and attack Donald Trump, the presumptive Republican presidential nominee. His first campaign stop with Mrs Clinton will be in Wisconsin on June 15.
In his video endorsement Mr Obama also praised Mrs Clinton for "the decision we made in the Situation Room to get Bin Laden".
Michelle Obama also endorsed Mrs Clinton. Josh Earnest, the White House press secretary, said: "The First Lady is enthusiastic about Secretary Clinton's campaign. You can certainly interpret that video as a joint endorsement."
After nearly eight years in the White House, Mr Obama's approval ratings, particularly among black, Hispanic, young, and liberal voters, remain high.
Mrs Clinton welcomed the endorsement, saying it "meant the world" to her and she was "thrilled".
She said: "It is absolutely a joy and an honour that President Obama and I, over the years, have gone from fierce competitors to true friends. He has my back in this election. I'm fired up and ready to go."
On Tuesday Mrs Clinton secured enough delegates to become the Democratic nominee.
Mr Obama praised Mr Sanders for an "incredible campaign" and for drawing young people into the political process. Shortly before releasing his video Mr Obama with Mr Sanders met for an hour in the Oval Office.
Afterwards, Mr Sanders refused to drop out immediately, saying he would continue to contest the final primary vote in Washington DC next week.
However, he said he would work with Mrs Clinton to defeat Mr Trump. He said: "I spoke to Secretary Clinton on Tuesday night and congratulated her on her very strong campaign. I look forward to meeting with her in the near future to see how we can work together to defeat Donald Trump."
Mr Obama added that it was a "healthy thing" for the party to have a contested primary, but acknowledged that the rift between the two candidates would not be smoothed overnight. He said: "My hope is that over the next couple of weeks is we're able to pull things together. The main role I'm going to be playing is to remind the American people that this is a serious job," he said. "This is not reality TV."
Mr Trump dismissed the president's endorsement of Mrs Clinton. He said: "Obama just endorsed Crooked Hillary. He wants four more years of Obama but nobody else does."