Democrat Vice Presidential nominee Kamala Harris brought the forensic skills of a prosecutor to the debate trying to overshadow incumbent Vice President Mike Pence as they faced off on the national stage, attempting to pin each other to policies they would avoid while deflecting hard questions.

The debate with a veneer of politeness on Wednesday night in Salt Lake City, Utah, was a marked contrast to the September 29 presidential debate where President Donald Trump was overbearing and traded insults with his Democratic rival Joe Biden.

A former prosecutor and the Attorney General of California, Harris was more at ease during the debate.

Harris, who is of Indian and Jamaican African descent, was expressive during the debate unlike the strait-laced Pence.

She made expansive gestures and her face reflected emotions as she spoke, and she sniggered or smiled deprecatingly while an almost wooden-faced Pence talked.

Both interrupted each other at times but got through it without rancor. They ended up with almost equal speaking time.

Harris tried to hang what she said were Trump's failings and mis-statements around Pence's neck, and he attempted to nail her to the Democratic Party's extreme left.

For Harris, it was also an audition for the presidency. Biden will be 78 years old if wins the election and is sworn-in in January, making him the oldest person to hold the presidency.

Harris is 55 years old and is widely expected to back him given his age and questions over his memory.

Although she has participated in Democratic debates while running for the party nomination – memorably hitting out at Biden on the race issue at one of them – this was the first time she was on a one-on-one debate with a national leader.

Harris recalled her mother and her Indian immigrant background when she spoke about the moment Biden asked her to be his running mate.

"I thought about my mother, who came to the United States at the age of 19, gave birth to me at the age of 25 at the Kaiser Hospital in Oakland, California. And the thought that I would be sitting here right now, I know, would make her proud. She must be looking down on this," she said.

"We were raised with values that are about hard work, about the value and dignity of public service, and about the importance of fighting for the dignity of all people."

Declaring victory, Biden tweeted: "Kamala Harris, you made us all proud tonight."

And Trump tweeted: "Mike Pence is doing great. She is a gaffe machine."

The debate was light on foreign policy, focusing on domestic issues like the COVID-19 pandemic that was center stage — metaphorically and literally, with Plexiglass partitions separating the debaters — the economy, abortion, climate change, the supreme court, race, and the conduct and outcome of the elections.

Pence was hard on China blaming it for the pandemic, the trade manipulation and the loss of jobs. Harris came off soft, criticizing Trump's "trade war" with China.

She said that according to Pew Research Centre leaders of US allies held Chinese President Xi Jinping in greater esteem than Trump.

While she talked of Trump endangering relations with Nato and other allies, Pence spoke of the President's initiative in the Indo-Pacific region.

Pence listed the US elimination of Islamic State chief Abu Bakr al-Baghdadi and Iranian General Qasem Soleimani under Trump and tried to make out that Biden was soft on terrorism saying that he had even opposed former President Barack Obama's action to take out Al Qaeda head Osama bin Laden.

Harris brought up the Russian interference in US elections and accused Trump of being subservient to Russian President Vladimir Putin.

Pence countered by accusing Harris and the Democrats of failing in their attempt to make the case that Trump colluded with Putin and of spying on the Trump-Pence campaign in 2016.

On the Covid-19 issue, Harris said that Trump was responsible for the more than 200,000 deaths because of his denial in public of its danger while privately acknowledging it and for the damage to the economy.

Defending Trump administration record, Pence said that a far less deadly swine flu had killed 49,000 people during Biden's watch.

Pence linked her and Biden to the left, repeatedly bringing up Biden saying that he would end fossil fuel and oppose the fracking method of extracting natural gas, and their backing for the Green New Deal, a radical agenda proposed by the radical wing of the party.

Harris said that Biden was not against fracking and disowned the Green New Deal for which she had been a legislative sponsor in Congress.

Debate moderator Susan Page of USA Today pointed out that the Green New Deal was still on the web page of the Biden-Harris campaign.

Pence boasted of the economic record under Trump till the Covid-19 pandemic intervened and said that Harris and Biden would damage the economy with their tax increases and the environmental agenda.

Pence reiterated his support for law enforcement while at the same time attacking Harris's role as a prosecutor leading to the disproportionate incarceration of minorities, with African-Americans and Latinos being prosecuted 19 times more than Whites for minor offences.

That was one time Harris showed a flash of anger. She was the only one in the room with experience of law of enforcement, she said.

"I will not be lectured by the vice president on our record of what we have done in terms of law enforcement and keeping our communities safe and a commitment to reforming the criminal justice system of America," she said.

Neither of them gave a straight answer to the moderator's question about what would they would do if Trump would not concede defeat in the election..