It's hardly a theoretical question: President Donald Trump, 74, is recovering from the coronavirus, and 77-year-old former Vice-President Joe Biden has not been infected but would be the oldest president ever.
For those reasons and more, the debate at the University of Utah in Salt Lake City may be the most meaningful vice-presidential debate in recent memory.
It comes at a precarious moment for the Republicans in particular, with growing concern that Trump's position is weakening as more than a dozen senior officials across the White House, the Pentagon and inside his campaign are infected with the virus or in quarantine.
Trailing in polls, Trump and Pence have no time to lose; Election Day is less than four weeks away, and millions of Americans are already casting ballots.
Before Harris says a word, she will make history by becoming the first Black woman to stand on a vice presidential debate stage. The night offers her a prime opportunity to energise would-be voters who have shown only modest excitement about Biden, a lifelong politician with a mixed record on race and criminal justice, particularly in his early years in the Senate.
Harris, 55, is the daughter of a Jamaican father and an Indian mother. She is also a former prosecutor whose pointed questioning of Trump's appointees and court nominees helped make her a Democratic star.
Pence is a 61-year-old former Indiana governor and ex-radio host, an evangelical Christian known for his folksy charm and unwavering loyalty to Trump. And while he is Trump's biggest public defender, the vice-president does not share the president's brash tone or undisciplined style.
Just eight days ago, Trump set the tone for the opening presidential debate, which was perhaps the ugliest in modern history. Today's affair is expected to be far more respectful.
Harris advisers say she does not plan to constantly fact-check Pence on stage and will instead spend her time making the case directly to the American people about what a Biden-Harris administration would offer.
"She's not there to eviscerate Mike Pence," said Symone Sanders, an adviser who has been in Harris' debate prep. "She is there to really talk to people at home."
Harris' team predicted she would focus on Trump's year-long efforts to downplay the pandemic, the fact that many schools are still closed and Trump's declaration this week that he would end talks on a fresh coronavirus economic relief package until after the election.
Harris will also have the chance to explain her views on law enforcement, an area in which she's irked some progressives, given her past as a prosecutor.
Pence aims to highlight the Administration's economic record and attempt to portray the Democratic ticket as beholden to the "radical left," former GOP Governor Scott Walker of Wisconsin, who is helping the Vice-President prepare for the debate, said.
Just as Harris will likely speak directly to Trump at times, Pence is likely to speak at Biden and progressives, who have called for a government run health care system known as "Medicare for All" and sweeping environmental reforms to combat climate change called the "Green New Deal." Biden opposes both plans in favour of more moderate steps that would still be among the most significant changes for health care and environmental policy in the modern era.
While the debate will cover a range of topics, the virus will be at the forefront.
- AP
