Mike Pence and Kamala Harris will line up on the vice-presidential debate stage in Salt Lake City, Utah on Wednesday separated by a plexiglass partition and with a key question hanging over their heads: "Are you ready to be president?"

In The Spotlight:

Mike Pence: Working in Trump’s shadow

Kamala Harris: Running mate defying labels

The understudies to, respectively, a 74-year-old Republican being treated for COVID-19 and a 77-year-old Democrat, will aim to demonstrate they have the skills and temperament to step into the top job if required.

The unprecedented situation, with President Donald Trump undergoing treatment for the virus at the White House and multiple members of his administration, including Press Secretary Kayleigh McEnany and senior adviser Stephen Miller, who is married to Pence aide Katie Miller, infected and military leaders in quarantine, puts the spotlight firmly on a one-off debate which typically takes place in the shadow of the top of the ticket. 

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Going into the 90-minute debate, CGTN analysis of public polls shows the Biden-Harris ticket leading Trump-Pence by 7.8 nationally and by smaller margins in the battleground states, with recent individual polls suggesting the Democratic duo receiving a boost after last week's Biden-Trump clash.

Why this one matters

Vice-presidential debates rarely live long in the memory, given that, like running mates, there's little historical evidence they make much difference to the outcome of the election.

The 2020 face-off has higher stakes: Pence heads the COVID-19 task force and is one step from the Oval Office at a time Trump is being treated for a deadly disease; Harris is the running mate to a man who would be the oldest president elected in history if he wins in November and is unlikely to run for a second term.

Pence, the 61-year-old Republican, would be in line to step in as acting president if Trump's condition worsens. With continued uncertainty over the president's health, Pence will be at the forefront of the campaign for the coming days and is scheduled to essentially take Trump's place on the campaign trail.

YouGov polling released on Monday suggested 65 percent of Republicans would also back the former Indiana governor to head the party's ticket in the election if the president is unable to do so.

Biden is a fit 77, but would nevertheless be the oldest president ever elected. Harris, the California senator and former prosecutor, will aim to reassure voters she has the experience and knowledge to be president.

There is also a chance, if Trump is not in a position to contest the remaining presidential clashes with Biden, that the Pence-Harris showdown will be the final set-piece TV event of the campaign, though Trump on Tuesday insisted he would spar with Biden on October 15.

The COVID-19 issue

The COVID-19 pandemic has been the central election issue for most of 2020 even as Trump has tried to downplay it and focus on more electorally favorable factors, such as the economy and his appointment of conservative judges.

But after a week in which the president was hospitalized and uncertainty over his condition continues, there's no getting away from the fact – however much he might wish it were not the case – that it is the issue on which most voters will cast their ballots.

Pence, the current vice president, chairs the COVID-19 task force which coordinated efforts to tackle the pandemic from the White House.

To the Republican's advantage heading into the debate, he has detailed knowledge of the government response which should help him parry some of Harris' criticisms, but he will still be asked to account for the deaths of over 210,000 Americans and the infection of around 7.4 million as well as the actions of Trump over the past week.

The former radio host also has more experience of the national spotlight than his rival after performing creditably against Democrat Tim Kaine in the 2016 VP debate and then spending nearly four years as Trump's deputy, often representing the president at events home and abroad.

Historically the running mate's role in campaign is to do the dirty work, attacking the opponent and defending the person at the top of the ticket. 

But Harris has a tough balancing act to play: critique the administration's handling of the pandemic without sounding unsympathetic to the condition of the president and those around him, while defending Biden's record and plans as well as her own. 

The 55-year-old has a reputation as a tough questioner after a spell on the Senate judiciary committee, but she has only been in Washington for four years and her previous debate experience is limited to state contests and mixed performances in the Democratic primaries. 

Precautions in place

Both candidates have tested negative for the virus, but the Commission on Presidential Debates (CPD) is taking no chances. Pence was at the nomination ceremony for Amy Coney Barrett where multiple members of the administration are thought to have contracted the virus, and Harris has been active on the campaign trail.

Not only will the candidates be seated at least 12 feet apart for the 90-minute debate, but plexiglass barriers will be placed between them as well as moderator Susan Page.

Page, Washington bureau chief at USA Today, is a veteran journalist who has covered 10 presidential elections. The debate is expected to follow a similar format to that intended in the first presidential debate, which descended into chaos as rules were ignored and insults flew.

All audience members will be required to undergo COVID-19 tests and wear masks throughout the debate – something several members of the Trump family refused to do at last week's clash. The CPD says anyone not wearing a mask will be removed from the event in Utah.

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