US President Barack Obama has given full-hearted support to Hillary Clinton in her bid to defeat Republican rival Donald Trump and become the first woman elected US president.
"There has never been a man or woman, not me, not Bill [Clinton] - nobody more qualified than Hillary Clinton to serve as president of the United States," Mr Obama said to cheers.
Speaking to the Democratic National Convention in Philadelphia, Mr Obama offered an alternative to Mr Trump's vision of the US as being under siege from illegal immigrants and terrorism and losing its way in the world.
"I am more optimistic about the future of America than ever before," Mr Obama told cheering delegates at the Wells Fargo Centre.
The Democratic president laid out what he said were a series of advances during his two terms in office, such as recovery from economic recession, the Obamacare healthcare reform and the 2011 killing of al Qaeda leader Osama bin Laden.
Nodding to voters' concerns, Mr Obama said he understood frustrations "with political gridlock, worry about racial divisions" and the slow pace of economic growth.
"There are pockets of America that never recovered from factory closures; men who took pride in hard work and providing for their families who now feel forgotten," Mr Obama said.
Senator Tim Kaine accepted the Democratic vice-presidential nomination earlier in the day.
Mr Obama and Mrs Clinton were rivals in the hard-fought campaign for the 2008 Democratic nomination. After winning that election, he appointed her his secretary of state.
Democrats have buttressed Mrs Clinton with a star gathering of current and past party notables at this week's convention. By contrast, many prominent Republicans were absent from the party convention that nominated Mr Trump for the White House last week.
But Mr Trump got a boost in opinion polls from his convention. He had a two-point lead over Mrs Clinton in a Reuters/Ipsos opinion poll released on Tuesday, the first time he had been ahead since early May.