Joe Biden, a moderate Democrat, who served eight years as Barack Obama’s vice president, is set to launch his third run for the White House on Thursday.

Biden will announce his bid by video, according to a source familiar with the plans. He then is expected to make his first public appearance as a candidate on Monday at an event in Pittsburgh featuring union members, a key constituency.

According to reports, Biden has made his appeal to the disaffected working-class voters who deserted the party in 2016 a key part of his political identity,

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 President Donald Trump, the likely Republican nominee, in November 2020.

Critics say Biden’s standing in polls is largely a function of name recognition for the former U.S. senator from Delaware, whose more than four decades in public service includes eight years as President Barack Obama’s No. 2 in the White House.

As speculation about his bid mounted, 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.

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.

Trump and his allies seized on the flap, attempting to weaken perhaps his top rival before Biden entered the race.

Even so, Biden was determined to push forward, arguing his background, experience and resume best positioned him to take on Trump next year.