WESTERVILLE, OHIO (AFP) - Twelve Democrats square off on Tuesday (Oct 15) in a crowded presidential debate overshadowed by an impeachment inquiry into United States President Donald Trump, who has dragged chief rival Joe Biden into the Ukraine crisis.
Will the front runners - Mr Biden, Senator Elizabeth Warren and Senator Bernie Sanders - extend their leads over the rest of the field, or will second-tier candidates desperate for a breakout moment vigorously challenge those at centre stage?
It is an extraordinary moment. Washington's impeachment brawl has dominated US politics for weeks and denied Democratic candidates the attention they crave ahead of what could be a pivotal showdown in the race to see who will face Mr Trump in 2020.
Mr Trump's July 25 phone call to his Ukrainian counterpart seeking help in investigating Mr Biden and his son, and the discredited charge by Mr Trump that the former US vice-president intervened in Ukraine to protect his son Hunter, has roiled the race and put Mr Biden in the spotlight.
The three-hour debate at Ohio's Otterbein University features Mr Biden, who is struggling to maintain front runner status, at centre stage with progressive Ms Warren, the only candidate steadily rising in the field and who is now nipping at his heels. Both are likely to face attacks from rivals.
Next is liberal Mr Sanders, who is under immense pressure to project fortitude two weeks after he was sidelined by a mild heart attack.
Joining them are South Bend, Indiana Mayor Pete Buttigieg; senators Kamala Harris, Cory Booker and Amy Klobuchar; former congressman Beto O'Rourke; entrepreneur Andrew Yang and Obama-era cabinet member Julian Castro.
Two others who missed the September debate but qualified for Ohio are congresswoman Tulsi Gabbard and billionaire activist Tom Steyer, who has sought Mr Trump's impeachment for two years.
The scandal over Mr Trump's communications with Ukraine has engulfed the White House, and will surely colour the debate proceedings.
An embattled Mr Trump has come out with guns blazing against Mr Biden and his son Hunter, repeatedly claiming without evidence that they are corrupt.
Mr Biden has begun criticising the President more forcefully, tweeting on Tuesday that "Trump is leading the most corrupt administration in modern American history".
But Mr Biden stands to lose perhaps the most in the Democratic dozen, as voters determine whether Mr Trump unfairly targeted him and his son, and if the latter's international work had the appearance of a conflict of interest.
Early on Tuesday, Mr Hunter Biden, who worked for a Ukrainian energy company when his father was vice-president, broke his silence, telling ABC News that while he may have exercised poor judgment in his business dealings in Ukraine and China, he broke no laws.
"Did I make a mistake based on some ethical lapse? Absolutely not," the 49-year-old, insisted.
Beyond the Trump impeachment fight, likely debate topics include healthcare, climate change, immigration, gun control and the economy.
Foreign policy is expected to loom larger than in previous debates, following Mr Trump's controversial troop pullout from northern Syria, which critics including virtually all Democratic candidates say green-lighted a Turkish invasion.
Ms Warren, meanwhile, takes the stage as the candidate on the rise, and the 70-year-old's performance will be closely watched.
Mr Sanders, a self-declared Democratic socialist, publicly distanced himself from his friend and fellow progressive for the first time on Sunday, saying there were "differences" between his outlook and Ms Warren's.
"Elizabeth I think, as you know, has said that she is a capitalist through her bones. I'm not," he told ABC's This Week. Mr Sanders, 78, is grappling with his own setback following a heart attack that put his health and age into question.
It tangentially raises concerns about Mr Biden, who turns 77 next month and has been criticised for lacking vitality in debates.
Ohio voted twice for Mr Barack Obama and then flipped to Mr Trump in 2016. Democrats are aiming to take it back next year.