The party's 76-year-old senior statesman is the most experienced and recognized Democrat in the race
Former US vice president Joe Biden jumped into the race for the White House Thursday, positioning the veteran Democrat as a frontrunner among the many candidates seeking to challenge Donald Trump in 2020.
The party's 76-year-old senior statesman is the most experienced and recognized Democrat in the race, a popular former vice president who has been dominating early polls following months - even years - of campaign planning.
In a tweet accompanied by a three-and-a-half minute video, Biden said he could not stand idly by as US President Donald Trump "fundamentally altered the character of this nation".
"The core values of this nation our standing in the world our very democracy everything that has made America - America - is at stake," he wrote in the post.
"That's why today I'm announcing my candidacy for President of the United States."
Biden, whose working-class appeal remains intact despite nearly half a century in Washington politics, is seen as a comforting, known quantity for American voters who will be vetting some 20 Democrats now officially in the presidential field.
But recent controversy over his tactile style, particularly with women, could dampen a rollout that he envisioned as the final main entry to the Democratic primary battle.
Even before his official announcement, Biden, who served eight years as Barack Obama's vice president, led most surveys of Democratic voters.
The RealClearPolitics poll aggregate puts him as favourite with 29.3% support, followed by independent Senator Bernie Sanders at 23%.
The record number of candidates means Biden finds himself in a field of unprecedented diversity as he makes his third run for president, following two unsuccessful attempts in 1988 and 2008.
After the death of his son Beau from cancer, Biden opted out of a presidential campaign in 2016.
As he let the suspense over his political plans drag out for months, his broad lead however has been whittled down, with newer and notably young faces gaining ground including moderate South Bend, Indiana Mayor Pete Buttigieg, who at 37 is less than half Biden's age.
Atop the polls
Complicating matters, the last weeks of waiting have been clouded by revelations from multiple women accusing Biden of touching them inappropriately or making them feel uncomfortable with his shows of affection.
Biden, an old-school politician who acknowledges he is quick to offer hugs and shoulder rubs as he forges connections with voters, has not outright apologized for his behavior, but he pledged earlier this month to be "more mindful" about society's changing boundaries.
After Biden and Sanders in the Democrat race, Senator Kamala Harris is third on 8.3%, followed by Buttigieg with 7.5%, progressive Senator Elizabeth Warren on 6.5% and former Texas congressman Beto O'Rourke 6.3%.
Biden leads the pack largely on the strength of his lifelong political experience - he was elected to the US Senate at just 29 - and his name recognition.
But in the early stages of what will be a heated primary battle, the status of frontrunner is by no means assured.
"The key question is whether Biden's current support represents more of a floor for him than a ceiling," Kyle Kondik of the University of Virginia's Centre for Politics told AFP.
"If it's a floor, he's in great shape. If it's a ceiling, his candidacy could fall apart quickly."
Shortly after the announcement, Obama praised Biden but avoided endorsing him.
Obama spokeswoman Katie Hill said: "President Obama has long said that selecting Joe Biden as his running mate in 2008 was one of the best decisions he ever made. He relied on the Vice President’s knowledge, insight, and judgment throughout both campaigns and the entire presidency. The two forged a special bond over the last 10 years and remain close today."
However, a source familiar with Obama’s thinking said the former president is not yet ready to endorse Biden.
"President Obama is excited by the extraordinary and diverse talent exhibited in the growing lineup of Democratic primary candidates. He believes that a robust primary in 2007 and 2008 not only made him a better general election candidate, but a better president, too," the source said.
"And because of that, it’s unlikely that he will throw his support behind a specific candidate this early in the primary process - preferring instead to let the candidates make their cases directly to the voters.”