Workers make final preparations on the set for the vice presidential debate to be held Tuesday at Longwood University in Farmville, Va. (Joe Raedle/Getty Images)

Tuesday night’s debate is between the No. 2’s — but it will be all about the No. 1’s.

Indiana Gov. Mike Pence (R) and Sen. Tim Kaine (D-Va.) will share the biggest and most hazardous stage of their careers when they face off in Farmville, Va., for the season’s only vice-presidential debate, and it is ­expected to center on the two figures atop the tickets.

Pence and Kaine are poised to duel over the temperament, qualifications, honesty and records of Republican Donald Trump and Democrat Hillary Clinton, as the two affable and smooth-talking men explain and proselytize for their historically unpopular running mates.

Pence has a particular challenge: Trump’s incendiary statements and erratic behavior, especially over the past week, have formed a hurricane at the center of the Republican campaign. Pence could be forced again and again to account for Trump’s actions.

“He’s got to be ready for how they come at him, whether it’s as some kind of rigid right-wing conservative or if they use the debate as a way to go after Donald’s tweeting or his position on immigration,” said former New York mayor Rudolph W. Giuliani, a close adviser to Trump.

The Washington Post’s Karen Tumulty explains what is at stake during vice-presidential debates before Tim Kaine and Mike Pence face off on Oct. 4. (Bastien Inzaurralde/The Washington Post)

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The debate, which begins at 9 p.m. on the campus of Longwood University, comes at a troubling time for Trump. He is reeling from a tumultuous performance in his first debate with Clinton last week, his attacks on a Latina beauty queen, his hostile 3 a.m. outbursts on social media and new revelations about his taxes.

“Mike Pence needs to go in there and try to change the trajectory of the race, but he can’t do that because the biggest problem with their campaign right now is the presidential candidate,” said Mo Elleithee, a former Kaine ­adviser who now directs Georgetown University’s Institute of ­Politics and Public Service.

Clinton spokesman Brian Fallon insisted that Pence will not be able to wash away the worries voters have about Trump’s temperament and qualifications: “No matter what type of performance Mike Pence turns in, it’s not going to resolve the underlying concerns.”

Historically, voters have tuned into vice-presidential debates to see whether the candidates — Sarah Palin, Dan Quayle and John Edwards, to name a few — appear prepared for the presidency should the need arise.

But Pence and Kaine seem to have met the governing threshold already with their lengthy tenures in elected federal and state offices. On the Republican ticket, for instance, Pence is more qualified for the presidency by traditional standards than Trump.

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Democratic vice-presidential nominee Tim Kaine greets supporters at a Labor Day campaign event in Cleveland on Sept. 5. (Melina Mara/The Washington Post)

Both vice-presidential nominees have been studying binders of issue briefings on their planes between campaign stops, and each spent the past few days ensconced with advisers gaming out possible lines of questioning and rehearsing answers. In their mock debates, Wisconsin Gov. Scott Walker (R) has been Pence’s stand-in for Kaine, while Washington super-lawyer Robert ­Barnett has been Kaine’s stand-in for Pence.

Kaine referenced the drudgery of his intensive debate preparations on the day after Clinton’s near-collapse at a Sept. 11 commemoration in New York. He recounted to an audience in Dayton, Ohio, that Clinton “started making fun of me because I was sitting reading endless debate prep memos.”

The debate’s setting in Farmville — which was chosen long before Clinton and Trump picked their running mates — gives the former Virginia governor a home-field advantage. Farmville was the epicenter of Virginia’s civil rights struggle, a point of resonance for Kaine, a former civil rights lawyer and the son-in-law of former governor Linwood Holton, who helped integrate Richmond’s schools in the 1970s. The state’s emergence from its segregationist past as a diverse economic powerhouse may give Kaine a dramatic backdrop against which to criticize Trump’s nationalist agenda and remarks.

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Tuesday will be the first face-to-face meeting for Kaine and Pence. When Kaine served as Virginia’s governor, Pence was working on Capitol Hill as a House member. They switched places in 2013, with Pence becoming Indiana’s governor and Kaine joining the Senate.

“We talked by phone once, but I never met him,” Kaine said in a recent interview. “He called and said, ‘Hey, welcome aboard.’ He had been on the ticket a week before me.”

Both No. 2’s have their future careers to consider during their turn Tuesday before what could be a national television audience of tens of millions. Pence, 57, has an eye on a possible 2020 presidential run, should Trump lose, while Kaine, 58, also has national ambitions, four or eight years from now.

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Ahead of Tuesday’s forum, there is pressure on Kaine and Pence to shore up their tickets by sending reassurances to key constituencies that remain skittish. Kaine could look to validate Clinton’s progressive credentials and make a hard sale to young voters, while Pence could use his evangelical roots to make overtures on Trump’s behalf to social conservatives.

Ralph Reed, founder of the Faith & Freedom Coalition, said Pence’s asset will be convincing churchgoing Republicans of Trump’s allegiance. “If he gets a slow, underhand pitch on a moral or cultural issue, you know he’ll be able to do really well with it,” Reed said. “There is no better ambassador for Trump among social conservatives.”

Pence and Kaine could be forced to explain some of the more controversial items in their records — such as Pence signing and later revising an Indiana religious liberties law last year that could have allowed businesses to refuse service to gay people, or Kaine’s work as an attorney defending suspected criminals, which was the subject of a video the Republican National Committee released Monday.

Pence and his advisers are anticipating that he will be put on the defensive over crude or racially charged things Trump has said and done — if not in the questioning from moderator Elaine Quijano of CBS News, then by Kaine.

“Why would Tim Kaine be the only person of the political-media axis who doesn’t make this campaign about Trump? Of course he will,” said Kellyanne Conway, Trump’s campaign manager and a longtime adviser to Pence.

Conway said Pence “knows the game” and will be ready to turn exchanges that begin about Trump matters into discussions about Clinton’s vulnerabilities.

“Mike Pence comes well prepared and ready to play,” Conway said. “He’s prepared to make the debate about the different visions, the failed policies [of Clinton], the past versus the future, more government versus less government, corruption and ethics, and certainly her record around the globe.”

[Mike Pence emerges as Donald Trump’s evangelist, emissary and explainer]

Pence has had an awkward time on the campaign trail cleaning up some of Trump’s more outlandish statements by testifying to the celebrity businessman’s heart as a family man and describing him as a “broad-shouldered leader” in the mold of Ronald Reagan.

“He’s not only defended Trump, but he’s running around talking about ‘this good man,’ which is ludicrous,” said Peter Wehner, who served in the administrations of the last three Republican presidents. “Mike Pence is an able guy. . . . But he’s going to look like a fool and twist himself like a pretzel to stand for a man who stands against most of what Mike Pence has stood for in his public life.”

Clinton aides said they are planning to exploit any daylight that might emerge between Pence and Trump, perhaps over Trump’s attacks on former Miss Universe Alicia Machado and the Gold Star parents of a Muslim U.S. soldier, or Trump’s years-long crusade questioning President Obama’s birth in Hawaii.

Trump prizes loyalty above all else in those around him, but Giuliani said he believes Trump would stand by Pence regardless.

“He thinks the world of Pence. Every time he sees him on television, he says, ‘Boy, I made a great choice,’ ” Giuliani said. “There’s no need to defend the candidate on everything. Nothing wrong with having a few disagreements.”

Pence, with his neatly cut white hair, tight smile and soft-spoken manner — “Rush Limbaugh on decaf” is an old nickname — will offer viewers a striking contrast with Trump.

“There is a saying in radio that the Midwestern accent is the best one,” said Rep. Peter T. King (R-N.Y.), a moderate who served with Pence in the House. “It gives people a peace of mind. That’s what Mike’s going to bring.”

Paul Kane and John Wagner contributed to this report.