Former US vice president Joe Biden has announced he is entering the 2020 White House race, joining an already crowded list of candidates running on the Democratic Party platform.
"The core values of this nation... our standing in the world... our very democracy... everything that has made America - America - is at stake," he said on Twitter.
"That's why today I'm announcing my candidacy for President of the United States," he added.
He is expected to make his first public appearance as a candidate on Monday at an event in Pittsburgh featuring union members, a key constituency.
Mr Biden, 76, had been wrestling for months over whether to run.
His candidacy will face numerous questions, including whether he is too old and too centrist for a Democratic Party yearning for fresh faces and increasingly propelled by its more vocal liberal wing.
Still, he starts as the leader of the pack in opinion polls of a Democratic field that now will total 20 contenders seeking the chance to challenge US President Donald Trump, the likely Republican nominee, in November 2020.
Critics say Mr Biden's standing in polls is largely a function of name recognition for the former US senator from Delaware, whose more than four decades in public service includes eight years as President Barack Obama's number two in the White House.
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. #Joe2020 https://t.co/jzaQbyTEz3
— Joe Biden (@JoeBiden) April 25, 2019
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Biden his time: Joe finally announces White House run
As speculation about his bid mounted, Mr Biden faced new questions about his longtime propensity for touching and kissing strangers at political events, with several women coming forward to say he had made them feel uncomfortable.
Mr Biden struggled in his response to the concerns, at times joking about his behaviour. But ultimately, he apologised and said he recognised standards for personal conduct had evolved in the wake of the #MeToo movement.
Mr Trump and his allies seized on the flap, attempting to weaken perhaps his top rival before Mr Biden entered the race.
Even so, Mr Biden was determined to push forward, arguing his background, experience and CV best positioned him to take on Mr Trump next year.
In a speech to union members in April, Mr Biden called Mr Trump a "tragedy in two acts".
"This country can’t afford more years of a president looking to settle personal scores," he said.
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