Former US vice-president Joe Biden has announced his third Democratic presidential bid.
He's become one of the most high-profile candidates to enter the busy race for the party's 2020 nomination.
Formally announcing his long-anticipated bid, he said: "The core values of this nation, our standing in the world, our very democracy.... everything that has made America America is at stake.
"That’s why today I’m announcing my candidacy for President of the United States."
Mr Biden - who spent more than three decades as senator before becoming Barack Obama's vice-president - unsuccessfully sought the Democratic presidential nomination in 1988 and 2008.
With the first primary votes due early next year, Mr Biden is expected to be one of the last high-profile candidates to enter the race.
Around 20 other candidates have formally declared, including a half dozen senators.
While opinion polls have consistently shown Mr Biden as an early favourite, candidates such as independent senator Bernie Sanders have gained momentum in recent months.
Multiple polls have indicated an extremely close race between Sanders and Biden, with both men having topped multiple recent polls.
With Biden widely considered a more traditional centrist candidate, he will be seeking the nomination over more progressive White House hopefuls such as Sanders and prominent senator Elizabeth Warren.
Like Sanders, the former vice president - who's currently 76, and would be 78 when taking office in early 2021 - is likely to face questions over his age during the campaign, amid a push from some for a younger candidate.
Younger hopefuls such as Beto O'Rourke and Pete Buttigieg have gained significant media attention in recent weeks after announcing their own bids.
Diversity issues are also likely to be prominent factors in the lengthy campaign, with a number of female and minority candidates hoping to secure the nomination.
Senator Kamala Harris has frequently been seen as one of the strongest contenders, frequently polling in third place behind Sanders and Biden.