Barring the unexpected, their 90-minute faceoff is unlikely to alter the trajectory of the presidential race.

Tuesday night’s vice presidential debate between Republican Gov. Mike Pence of Indiana and Democratic Sen. Tim Kaine of Virginia pits a former radio host who’s described himself as ‘‘Rush Limbaugh on decaf’’ against a harmonica-playing former missionary whose aw-shucks style has spawned a thousand dad jokes.

WASHINGTON — We interrupt this year’s slugfest between Donald Trump and Hillary Clinton to bring you their understudies: two low-key, middle-aged guys.

But don’t hit the snooze button just yet. Debate history suggests there still is the potential for some memorable moments.


Some things to watch for in Tuesday’s debate at Longwood University in Farmville, Virginia.

Say who?

Pence and Kaine have campaigned full tilt for more than two months now, but plenty of people still don’t have a feel for them. In a recent Associated Press-GfK poll, more than half of registered voters said they didn’t know enough about Kaine to venture an opinion about him, and about 44 percent said the same for Pence. This is their big moment to show they’re qualified to be next in line to the president.

Scout motto

Trump may disdain traditional debate prep, but Kaine and Pence both have embraced the Scout motto: Be prepared. Each must be ready to defend his own record, skewer his opponent and do the same for the top of the ticket.

The mission

Pence and Kaine have to decide whether to focus more on one another or on Trump and Clinton. Watch how they toggle between the two tasks. Look for Pence, who calls Clinton ‘‘the most dishonest person ever to seek the presidency,’’ to zero in on lines of attack that Trump hardly touched in the first debate, such as questions about whether Clinton played favorites as secretary of state with donors to the Clinton Foundation. Kaine will try to act as a character witness for Clinton and go after Trump, of whom the senator says his ‘‘only recognized passion in his life has been for himself.’’


Defending the indefensible

Pence will have the added herculean task of explaining away the steady stream of insults, barbs and inflammatory comments delivered by his running mate, including the latest contretemps over a beauty queen whom Trump has shamed for gaining weight. Pence has had plenty of practice in recent weeks. Expect him to employ a strategy of praising Trump for his unscripted style as a ‘‘bold truth teller’’ without arguing the merits of the GOP nominee’s specific comments.

Threading the needle

Both candidates may need to navigate areas where they have policy differences with their running mates; Pence more so than Kaine. Pence, for example, says it’s clear that human activity is affecting the climate while Trump has called global warming a hoax. Kaine holds that U.S. military operations against the Islamic State group have not been properly approved by Congress, a point of disagreement with Clinton.

Amen corner

Expect both Pence, an evangelical, and Kaine, a former Catholic missionary, to showcase their religious backgrounds in an effort to appeal to different constituencies. Pence likes to say of himself: ‘‘I’m a Christian, a conservative and a Republican — in that order.’’ Kaine often brings up his time as a missionary in Honduras, working in a few lines of Spanish along the way to reach out to Hispanics.

Too clever?

Past vice presidential debates have provided some memorable lines. Republican Bob Dole’s cutting quip in 1976 about all the Americans killed in ‘‘Democrat wars’’ did him no good. Democrat Lloyd Bentsen’s 1988 putdown of Republican Dan Quayle with his ‘‘You’re no Jack Kennedy’’ line still singes. Third-party candidate James Stockdale’s rambling 1992 opening questions of ‘‘Who am I? Why am I here?’’ captured a candidate who was clearly out of his element. Four years ago, Vice President Joe Biden’s denunciations of Republican Paul Ryan’s budget math as ‘‘a bunch of malarkey’’ showed considerably more spark than did President Barack Obama’s leaden performance against rival Mitt Romney in the leadoff debate.


Moderation

CBS News’ Elaine Quijano will be under the microscope as moderator, especially since Trump has complained that NBC’s Lester Holt, the moderator of last week’s debate, was too tough on him.

Associated Press writers Kathleen Ronayne in Raleigh, North Carolina, and Alan Suderman in Richmond, Virginia, contributed to this report.