WASHINGTON (AFP) - White House hopeful Joe Biden faces a new test Thursday (Dec 19) as he takes on six Democratic rivals in the latest prime-time debate of a 2020 race until now overshadowed by the impeachment of US President Donald Trump.
Just seven of the 15 Democrats still in the nomination race have qualified to make their pitch to voters at Loyola Marymount University in Los Angeles, six weeks before the first ballots are cast in Iowa.
And even those qualified may struggle to stand out on the issues, as the all-consuming drama surrounding Trump's impeachment continues to suck political oxygen from the White House campaign.
Trump was impeached in the Democratic-controlled House of Representatives on Wednesday for abuse of power and obstruction of Congress.
One day later, the spotlight is already swinging to the Senate trial, where the billionaire president is expected to be acquitted by a Republican majority.
Biden himself is a key character in the impeachment saga, which centres on Trump's attempts to pressure the president of Ukraine to investigate the former vice president and his son Hunter - which Democrats said amounted to soliciting foreign interference in next year's vote.
For despite campaign gaffes, doubts about his health and age - 77 - and the repercussions of the Ukraine affair, Biden remains the favorite to face off against Trump in November.
Biden currently enjoys 27.9 per cent support among likely Democratic voters, according to a poll average by the RealClearPolitics website.
A centrist, he promises to take America back to the way things were under Barack Obama, rescuing it from the extreme polarisation that has characterised Trump's tenure. He is popular with blue collar workers and African Americans.
"I look forward to joining the debate tomorrow to discuss how I'll strengthen our unions and build an inclusive middle class," he said on Twitter Wednesday.
Keen to quiet concerns about his health, Biden on Tuesday released a statement by his physician attesting to his good health, vigour and fitness "to successfully execute the duties of the Presidency."
In a rare display of temper, he recently lashed out at a man in an Iowa town hall audience who accused him of arranging a job for his son Hunter with a Ukrainian gas company.
"You're a damn liar, man," Biden said.
Behind him in the polls are Vermont Senator Bernie Sanders (19.7 per cent) and Massachusetts Senator Elizabeth Warren (15 per cent), who are competing for the party's progressive wing.
Their leftist platform - universal health care, a tax on the wealthy to reduce inequality, action on climate change - is very popular with young and women voters, but makes moderates uneasy.
Centrist Pete Buttigieg, the first gay candidate with a real chance to win the White House, is in fourth place with 8.6 percent.
The young mayor of South Bend, Indiana has surged since October in Iowa, a key state because it votes first in the Democratic nominating process on February 3. He also has recently shown strength in New Hampshire, which votes next on February 11.
Further back in the pack is entrepreneur Andrew Yang at 3.4 per cent, followed by Minnesota Senator Amy Klobuchar (3.2 per cent) and California billionaire Tom Steyer (1.4 per cent).
Also hovering over the debate is the race's newest entrant, former New York mayor Michael Bloomberg, a billionaire who is using his personal fortune to fund his own campaign.
He is polling at 5.1 per cent but doesn't have the minimum 200,000 individual donors required by the debate organizers. Having announced his candidacy very late in the campaign, Bloomberg is focusing on the 15 states that vote in early March, including Texas and California.
At one point, the debate was threatened by a strike by university cafeteria workers. But the dispute was settled on Tuesday, thanks to mediation by Democrats.