Kamala Harris on Wednesday assailed Donald Trump's response to Covid-19 as a failure in a high-stakes debate with Vice President Mike Pence against the backdrop of the president's own infection.

With Pence first in line for the presidency should Trump be unable to perform his duties, and Harris essentially auditioning to be the Democratic Party's future leader under a President Joe Biden, their pandemic showdown took on fresh urgency 27 days before the election.

Mike Pence, Kamala Harris debate
Vice President Mike Pence and Kamala Harris's showdown has taken on an unusually pressing quality given President Donald Trump's coronavirus diagnosis, with the White House deputy just a heartbeat away from the presidency Photo: AFP / MANDEL NGAN

"The American people have witnessed what is the greatest failure of any presidential administration in the history of our country," Harris, a US senator from California and former prosecutor, said in the first moments of the debate in which the candidates were separated by plexiglass.

Saying Trump treated front-line health personnel as "sacrificial workers," Harris -- pointing to Trump's own statements to journalist Bob Woodward -- accused the White House of not taking action despite knowing the risks of Covid-19.

"The president said it was a hoax. They minimized the seriousness of it," Harris said.

Mike Pence, Kamala Harris debate
US Vice President Mike Pence and Democrat Kamala Harris will be separated by a plexiglass barrier when they sit down for their vice presidential debate in Salt Lake City, Utah Photo: AFP / Eric BARADAT

After a raucous debate eight days ago between Trump and Biden, Pence and Harris initially took a more civil tone, with no name-calling, but sharply disagreed on the reaction to the pandemic.

"I want the American people to know, from the very first day, President Donald Trump has put the health of America first," Pence said, pointing to his ban on travel from China on January 31, a month after cases first emerged in Wuhan.

Referencing a controversy that tanked Biden's first presidential campaign in 1988, Pence said the Democrats' Covid plan sounds "a little bit like plagiarism, which is something Joe Biden knows a little bit about."

Mike Pence, Kamala Harris debate
Key dates in the lives of US Vice President Mike Pence and Democratic Party vice presidential Kamala Harris. Photo: AFP / Kun TIAN
Mike Pence, Kamala Harris debate
People stroll around the University of Utah campus in Salt Lake City on October 7, 2020, where police officers are watching the scene before the start of the vice-presidential debate between Mike Pence and Kamala Harris Photo: AFPTV / Sébastien VUAGNAT

Two more presidential debates are scheduled, but they are now up in the air with Trump's diagnosis, meaning the debate between the running mates could potentially become the final candidate clash before November 3.

Biden, 77, has said he would not want to debate if the 74-year-old Trump -- confined to the White House after a three-night hospitalization -- is still sick with the virus.

But Trump, ever the hyperbolic showman, said in a Wednesday video that he felt "perfect."

Kamala Harris
SOUNDBITESenator Kamala Harris brands the response to the Covid-19 pandemic under Donald Trump as the "greatest failure" of any US administration, as the debate between her and Vice President Mike Pence opens. Photo: US POOL

"I think this was a blessing from God that I caught it," he said, explaining that his diagnosis provided opportunities to highlight therapies that he was administered and would like more Americans to receive.

In a nod to medical concerns, Harris and Pence were sitting 12 feet (3.6 meters) apart for the 90-minute debate at the University of Utah, with the plexiglass set up despite pushback from the Trump campaign.

Asked by reporters Wednesday if he had advice for his running mate on one of the biggest political stages of her career, Biden said, "I think she'll do well."

Harris, if elected, would make history by becoming the highest-ranking woman in US history and both the first African-American and Asian-American vice president.

The debate occurs at a time when more than 210,00 Americans have died from the coronavirus and the nation lurches from one crisis to another.

Not only has Trump tested positive; coronavirus has spread through his inner circle, infecting dozens of top advisors, administration staff, senior military officials and Republican lawmakers.

Racial and political tensions are simmering, prompting Biden to issue a clarion call for national unity and warn that "the forces of darkness" and division are "pulling us apart."

Trump continued his all-out verbal offensive, branding Biden "a wacko" in a stream of angry tweets Wednesday.

The president is confronted by dire polling numbers and an economy staggering from Covid shutdowns that have left countless families and businesses struggling.

The unique political storm led Republican Senator John Barrasso to describe the Pence-Harris showdown as "the most consequential vice-presidential debate since they started doing this," in 1976.

"People watching both of these candidates will be watching to see who is ready to be commander-in-chief," Barrasso told CNN.

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