An emotional Joe Biden wiped away tears as he prepared to deliver a farewell speech to his party’s members.
Ahead of what’s been billed as the outgoing president’s swansong, Mr Biden was introduced to the stage at the Democratic National Convention in Chicago by his daughter Ashley.
A visibly moved Mr Biden was greeted by a more than four-minute-long ovation and chants of “thank you Joe”, with the 81-year-old saying: “I love you.”
Latest as tearful Biden says democracy must be preserved
He warned democracy “must be preserved” and urged the crowd to get behind Kamala Harris, who replaced him as the party’s candidate for the November election a month ago.
“Democracy has prevailed, democracy has delivered and now democracy must be preserved,” he said, later referring to Republican candidate Donald Trump as a “loser”.
He added the US is at an “inflection point” and this election will determine the fate of the nation and the world for “decades to come”.
Mr Biden abandoned his bid to remain as president a month ago after a series of gaffes and a disastrous debate performance against Mr Trump, with Kamala Harris stepping in as candidate.
US First Lady Jill Biden said her husband dug “deep into his soul” when he decided not to run for re-election, adding Ms Harris’s “courage” and “leadership” will win the race to the White House.
Ms Harris herself made a surprise appearance, drawing cheers from the crowd as she vowed to defeat Mr Trump in the November election.
“Let us fight for the ideals we hold dear and let us always remember, when we fight we win,” the US vice president said in brief remarks.
She also paid tribute to Mr Biden, thanking him for “historic leadership” and a “lifetime of service” to the nation.
Hilary Clinton, whose loss to Mr Trump in the 2016 election ended her hopes of becoming the first female US president, said Ms Harris can succeed where she could not.
“Kamala has the character, experience and vision to lead us forward,” she said, after entering to a standing ovation.
Mrs Clinton also took shots at her former nemesis, who became the first former US president to be criminally convicted in May.
“Donald Trump fell asleep at his own trial, and when he woke up, he made his own kind of history, the first person to run for president with 34 felony convictions,” she said.
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While Democrats gathered for their convention, thousands of people assembled at a nearby park to protest the party’s military support for Israel’s Gaza offensive.
The protesters were fewer than the tens of thousands organisers predicted, but a splinter group left the main march and breached a security perimeter near the convention centre, with riot police detaining four people.