Atlanta (AFP) - The top Democrats in the 2020 presidential nomination race clashed over health care and other priorities in Wednesday's debate, laying bare their divide between moderate and liberal policy platforms.

After an opening phase dominated by talk of impeachment of Donald Trump, participants in the fifth Democratic debate locked horns over health care, in particular the costly universal coverage program supported by liberal senators Elizabeth Warren and Bernie Sanders.

"The fact is that right now the vast majority of Democrats do not support Medicare for All," frontrunner and former vice president Joe Biden said.

"It couldn't pass the United States Senate right now with Democrats. It couldn't pass the House."

Biden proposes building on the existing Obamacare and adding an public option for health care, and "not make people choose."

Pete Buttigieg, currently the ascendant candidate in the race and who is running in the same moderate lane as Biden, said Democrats can seize a majority on issues like immigration and guns, "if we can galvanize, not polarize that majority."

On health care he too attacked the liberals, saying government should not be "commanding people" to accept Medicare for All.

"Whether we wait three years as Senator Warren has proposed or whether you do it right out of the gate is not the right approach to unify the American people around a very, very big transformation that we now have an opportunity to deliver," said Buttigieg, who is the mayor of the small town of South Bend, Indiana.

The health debate is at the center of the political divide between the candidates.

Warren has made headway by pledging to end a system that is working "better for... the rich and well-connected, and worse and worse for everyone else."

"I'm tired of freeloading billionaires," she said.

Biden leads in national polling, followed by Warren and Sanders.

But the three septuagenarian political veterans are seeking to blunt the surge of 37-year-old Buttigieg, a military veteran and the first gay candidate with a viable shot at the White House, as anxiety builds about who will challenge Trump.

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Buttigieg is cracking into the top tier with a steady rise in the past month, particularly in early-voting states like Iowa where he has seized the momentum.

His unruffled campaign demeanor and pragmatic reform proposals have gained traction in Iowa and New Hampshire, the two states that vote first in the nomination race.

But even as the 10 qualifying candidates rumbled in their nationally televised showdown in Atlanta, dominating the political discourse is the high-stakes impeachment hearings into Trump's dealings with Ukraine.

Democrats accuse Trump of conditioning military aid and a White House meeting on Kiev's announcing investigations of Biden and his son Hunter, who worked with a Ukrainian energy company while his father was vice president.

Testifying just hours before the debate, Gordon Sondland, ambassador to the European Union, said he was ordered by Trump to seek a deal in which Ukraine would probe Biden in exchange for a White House meeting.

But some candidates warned that obsessing over the president's alleged corruption and wrongdoing could sabotage Democrats' efforts.

"We cannot simply be consumed by Donald Trump," Sanders said. "Because if we are, you know what? We're going to lose the election."

- Democratic anxiety -

With national attention directed at Capitol Hill, the debate run-up has been low-key.

Ten qualified for Wednesday's debate: Biden, Warren, Sanders and Buttigieg; senators Kamala Harris, Cory Booker and Amy Klobuchar; entrepreneur Andrew Yang and investor-turned-activist Tom Steyer; and congresswoman Tulsi Gabbard.

The field may soon expand to include billionaire businessman and former New York mayor Michael Bloomberg who has recently filed ballot paperwork in two states.

Bloomberg's entry could signal lack of confidence in Biden's candidacy -- and a broader sense of anxiety among Democrats about whether their party will nominate the right candidate to defeat Trump.

Biden's floundering campaign could benefit Buttigieg, who occupies the same centrist lane.

Nationally, Buttigieg is in fourth position, according to a RealClearPolitics polling average.

But a recent Des Moines Register poll of Iowa voters showed him storming into the lead with 25 percent support, followed by Warren at 16 percent and Biden and Sanders at 15 percent.