US Vice President Mike Pence and Democratic vice presidential nominee Kamala Harris are set to face off in their only debate, as Donald Trump's coronavirus diagnosis and the pandemic continue to roil the US presidential contest.

The televised encounter in Salt Lake City, Utah, comes after the Republican president announced last Friday that he had tested positive for the coronarivus amid a White House outbreak.

Former Vice President Joe Biden, the Democratic presidential nominee, is leading Trump in national polls, including an advantage of 12% points in the latest Reuters/Ipsos survey of likely voters, with less than four weeks until the 3 November election. 

Polls show the race to be closer in some of the election battleground states that could determine the winner.

The two campaigns have squabbled over installing barriers onstage between Mr Pence and Ms Harris to guard against infection. Early today, television images of the debate stage showed two plexiglass barriers, one adjoining each lectern.

Ms Harris had requested plexiglass shielding. Mr Pence spokeswoman Katie Miller on Monday mocked Ms Harris, saying if she "wants to use a fortress around herself, have at it".

Both Mr Pence and Ms Harris, a US senator from California picked by Mr Biden in August as his running mate, tested negative for the coronavirus yesterday. Current US government guidelines call for anyone exposed to a person with Covid-19 to quarantine for 14 days regardless of test results.

In a statement, Ms Harris spokeswoman Sabrina Singh said: "If the Trump administration's war on masks has now become a war on safety shields, that tells you everything you need to know about why their COVID response is a failure."

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With two septuagenarians at the top of the ballot – Mr Trump is 74 and Mr Biden is 77 - the debate could take on greater importance. Mr Pence, 61, and Ms Harris, 55, will seek to demonstrate that they could step into the Oval Office if necessary to lead the country. 

Mr Pence has been an ardent defender of Mr Trump during his tumultuous presidency.

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Mr Trump returned to the White House on Monday after three days at Walter Reed National Military Medical Center in Maryland. It is unclear when he will again be able to campaign. 

Yesterday, he said he looked forward to the 15 October presidential debate, the second of three scheduled encounters with his Democratic rival.

The pandemic is likely to dominate the Pence-Harris debate. Mr Biden and Ms Harris have made Mr Trump's handling of the public health crisis a central theme of their campaign, blaming Mr Trump for downplaying the health risks and failing to endorse mask-wearing to combat the spread of the pathogen.

Mr Pence, who has headed up the administration's coronavirus task force, can be expected to defend Mr Trump's response to the pandemic, which has killed more than 210,000 Americans and battered the US economy even as other wealthy nations have managed to get it under better control.

Viewers will have a constant reminder of the pandemic's effect on daily life. Mr Pence and Ms Harris will be placed more than 3.6 meters apart on stage at the University of Utah, in addition to the plexiglass barrier.

In preparation for the debate, Ms Harris received help from former Democratic presidential primary rival Pete Buttigieg, a former mayor of South Bend, Indiana, who is familiar with Mr Pence's past record when he was governor of the Midwestern state.

The debate is unlikely to match the chaos of the first presidential debate last week in which Mr Trump repeatedly interrupted Mr Biden and the two traded insults. 

Mr Pence, who once hosted a radio show, and Ms Harris, a former prosecutor known for sharp questioning during Senate hearings, are seen as polished communicators.

A Biden campaign official said Ms Harris has prepared for Mr Pence to attack her as too liberal, which would echo Mr Trump's assertion that the moderate Mr Biden would advance a "radical left-wing" agenda if elected president.

The debate will be live on the RTÉ News channel from 2am and will be repeated from 9am tomorrow morning (Irish time).

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