Vice President Mike Pence squares off against Kamala Harris, his Democratic challenger for the office, in their lone debate Wednesday, with the deputy’s duties and succession powers suddenly prominent as President Donald Trump battles COVID-19.

The sedate Pence will face one of the biggest nights of his political life as Americans mull the possibility of the behind-the-scenes expert being asked to assume the duties of the president — or even take the lead in an election race that has been almost entirely about Trump.

It would be a profound pivot for someone forced into the background during Trump’s brash and calamitous presidency.

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“The stakes in this election have never been higher. The choice has never been clearer,” Pence said Monday as he headed to Salt Lake City, Utah, site of his debate with California senator Harris, who is Democratic nominee Joe Biden’s running mate.

“And I look forward to the opportunity to take our case to the American people for four more years of President Donald Trump.”

Four years ago, Democrat Hillary Clinton’s running mate Tim Kaine derided Pence as “Trump’s apprentice” during their debate, but the Republican delivered a more polished performance than his rival.

Pence and Harris have both tested negative for the virus since Trump’s positive diagnosis Friday. But they are fiercely divided in their response to the virus that has killed more than 210,000 Americans.

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Harris, 55, wears a face-covering in public, while Pence hews more to Trump’s maskless approach, including at a recent Rose Garden ceremony attended by several administration officials and lawmakers who have since tested positive.

Pence has been crucial to Trump’s administration, a pillar of stability in a White House that has churned through top officials, and a magnet for a part of the Republican base dubious of the fickle New York real estate tycoon.

A lawyer by training and former radio talk show host who served in Congress for 12 years, Pence was governor of Indiana in 2016 when Trump recruited him as his running mate.

The white-haired 61-year-old brought credibility as a traditional evangelical Christian who could appeal to church-going Americans and farm-belt conservatives.

The yin to the president’s yang: where Trump is loud and offensive, Pence is taciturn and mannerly; where Trump flouts morality, Pence is deeply pious.

Where Trump’s life has featured three wives and many more girlfriends, Pence is famous for abiding by a Christian rule that forbids him from being alone with any woman who is not his wife.

After taking office, Pence let Trump hold the entire stage.

He toiled quietly on important jobs such as liaising with Congress and Republicans and undertaking significant diplomatic missions.

And he smoothly adapted his earlier political stances to Trump’s china-shop-smashing approach to trade, diplomatic relations and immigration.

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In early trips to Europe and Asia, he set the stage for Trump’s policy resets while reassuring allies worried about the president’s ballistic rhetoric.

Pence stayed a team player, never betraying differences with Trump or promoting himself — sins that cut short the careers of others in Trump’s Cabinet.

That didn’t change in March when Pence was named as the public face of the White House coronavirus task force.

Echoing Pence’s own personality, the scientist-heavy group’s daily briefings sought to introduce calm, clarity and rigour to public information — but only until Trump hijacked them and undermined their messages about social distancing, face masks and treatments.

Pence’s motive has never been clear. Has he been, like many vice presidents, biding his time for his own shot at the presidency?

Or does he tolerate Trump, like many Republicans, because in his position he can advance the social conservatives’ agenda?

Earlier this year, there was speculation that Trump — facing an uphill fight for reelection — would replace Pence with someone who might excite more voters, such as former UN ambassador Nikki Haley or Secretary of State Mike Pompeo.

In the end, the odd couple stuck together, with Trump hailing his number two as “solid as a rock” in August.