Pence and Harris are set to take the stage at the University of Utah in Salt Lake City separated by plastic barriers for a 90-minute debate, a reminder of how the coronavirus pandemic has affected the race ahead of the November 3 election.
The Republican president announced last Friday that he had tested positive for the novel coronavirus amid a White House outbreak and was hospitalized in Maryland for three days receiving a variety of treatments. His doctor said on Wednesday Trump had no COVID-19 symptoms in the past 24 hours.
Either Pence, 61, or Harris, 55, would be a heartbeat away from assuming the presidency, depending on the election's outcome. How they handle themselves during the debate may be scrutinized even more closely than usual given Trump's health and the age of both presidential candidates.
Now 77, Biden would be 78 upon taking office in January, which would make him the oldest US president in history. Trump is 74, making his COVID-19 particularly dangerous considering his age and underlying health issues. Trump already is the oldest president to seek re-election.
Biden is leading Trump in national polls, including an advantage of 12 percentage points in the latest Reuters/Ipsos survey of likely voters. Polls show the race to be closer in some of the election battleground states that could determine the winner, although a Reuters/Ipsos poll on Wednesday showed Biden leading Trump in pivotal Florida.
Harris, who will be on the biggest stage of her political career, is a US senator from California picked by Biden in August as his running mate. The daughter of immigrants - her father from Jamaica and her mother from India - Harris is the first Black woman nominated by a major party for vice president as well as the first person of Asian descent.
Pence, who debated then-Democratic vice presidential nominee Tim Kaine in 2016, is a former US congressman and Indiana governor who has steadfastly defended Trump during his tumultuous presidency.
Their debate is unlikely to match the chaos of the first presidential debate last week in which Trump repeatedly interrupted Biden and the two traded insults. Pence, more even-tempered than Trump, and Harris, a former prosecutor known for sharp questioning during Senate hearings, are seen as polished communicators.
'A FORTRESS'
The two campaigns have squabbled over installing barriers on stage between Pence and Harris to guard against coronavirus infection. On Wednesday, television images of the debate stage showed two plexiglass barriers, one adjoining each lectern. Pence and Harris also will be placed more than 12 feet (3.6 meters) apart on stage.
Harris had requested plexiglass shielding. Pence spokeswoman Katie Miller on Monday mocked Harris, saying if she "wants to use a fortress around herself, have at it." An aide to the vice president on Wednesday said Pence had agreed to the barriers to facilitate the debate.
Both Pence and Harris tested negative for the coronavirus on Tuesday. 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, 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."
The pandemic is likely to dominate the debate. Biden and Harris have made Trump's handling of the public health crisis a central theme of their campaign, blaming Trump for downplaying the health risks and failing to endorse mask-wearing to combat the spread of the pathogen.
Pence, who has headed the administration's coronavirus task force, can be expected to defend 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.
A Biden campaign official said Harris has prepared for Pence to attack her as too liberal, which would echo Trump's assertion that the moderate Biden would advance a "radical left-wing" agenda if elected president.