ATLANTA (AP) — Republican JD Vance and Democrat Tim Walz will meet Tuesday in the lone vice presidential debate of the 2024 election, bringing together undercards who have spent two months going after each other and the opposing nominees who top the major-party tickets.

The matchup, hosted by CBS News in New York, might not carry the same stakes as the Sept. 10 debate between former President Donald Trump and Vice President Kamala Harris. But it offers their top lieutenants a fresh opportunity to introduce themselves, vouch for their bosses and fulfill a time-honored role of a running mate: attack dog. It will involve the biggest television and online audience either No. 2 will see before Election Day.

Walz, the 60-year-old Minnesota governor, and Vance, a 40-year-old U.S. senator from Ohio, have previewed potential approaches for weeks. Walz, before Harris selected him, was the Democrat who coined “weird” as a go-to pejorative for the Republican ticket. Vance assails the governor’s progressive record as proof Democrats are too far left for voters.

Vance has mocked his fellow veteran’s military service record. Walz hammers Vance’s opposition to abortion rights and his views on family life. Both men have played up their small-town, middle-America credentials — contrasts to Trump, the billionaire native New Yorker, and Harris, the California Bay Area native.

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It sets up a potentially fierce night in Manhattan. Here are the dynamics to consider as the rivals meet face-to-face for the first time:

Is it more Walz vs. Vance or Harris vs. Trump?

Running mates have a balancing act. Their primary job is to make the case for their bosses. But a vice presidential nominee’s credibility and connection with the audience are important factors in reaching that goal. If a voter doesn’t like the messenger, they’re less likely to buy the message.

Going into the debate, a new AP-NORC poll suggests Walz is better liked than Vance, giving the Republican perhaps a steeper challenge.

The poll found that only a quarter of registered voters have a somewhat or very favorable view of the Ohio senator, while about half have a somewhat or very unfavorable view. About a quarter don’t know enough to say. Walz is viewed positively by about 4 in 10 voters and negatively by about 3 in 10; the rest don’t know enough to say.

Still, Sen. Tim Kaine, a Virginia Democrat and the 2016 vice presidential nominee, warned participants against thinking too much about themselves.

“The only advice that matters is to protect the top of the ticket,” Kaine insisted, recalling the 2000 matchup between Republican Dick Cheney and Democrat Joe Lieberman. “Cheney kept attacking (Al) Gore, and Lieberman, instead of defending Gore, tried to make himself likable. ... You can’t leave attacks unanswered.”

Abortion rights and views on family will feature prominently

Democrats believe abortion rights and reproductive health care will motivate their core voters and sway swing voters.

Walz has tried to capitalize already by mixing his story into the argument. The governor talks often about how he and his wife, Gwen, required fertility treatments to have their daughter. Democrats have excoriated Vance for his 2021 quip about “childless cat ladies” shaping American life. And Walz has been eager to echo Harris’ emphasis on abortion rights as an anchor of her overall campaign theme: “Freedom.”

Vance and Trump, on the other hand, have struggled for a consistent message on abortion rights — a reflection of how politically fraught the issue is for Republicans since support for abortion access has increased since the 2022 Supreme Court decision to overturn Roe v. Wade and end a woman’s constitutional right to terminate a pregnancy. Trump brags about appointing conservatives who helped strike down Roe and return abortion regulation to state governments. Many Republicans now want to go beyond state bans and place federal restrictions on the procedure, but Trump has indicated that overturning Roe is enough. He has also waffled on how he’ll vote on a Florida referendum that would expand abortion rights.

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Vance said in August that Trump would veto a national ban if it cleared Congress. A couple of weeks later, during Trump’s debate with Harris, the former president demurred on an answer, saying, “I didn’t discuss it with JD.” The Harris campaign has amplified audio of Vance saying as a Senate candidate that he would like to see abortion outlawed nationwide.

Vance and Walz are competing for an advantage on the economy

Vance often offers clearer arguments than Trump about boosting American manufacturing, helping workers and punishing corporations. He regularly attacks the Biden-Harris administration over inflation. If there’s a broad topic where Vance wants to put Walz on the defensive and tether the Democratic ticket to President Joe Biden, it’s the economy.

For her part, Harris declares that “building the middle class will be a defining goal of my presidency.” She acknowledges many consumers’ struggles even as she generally defends Biden’s overall record of economic growth, low unemployment and rising wages since inheriting a COVID-19 freefall.

Both campaigns have competing suites of economic proposals, including varying tax cuts and subsidies for certain sectors. Expect the running mates to spend considerable time trying to convince the dwindling slice of persuadable voters that their ticket is more in tune with most U.S. households’ day-to-day economic concerns.

The two are expected to talk up their middle-America roots

As much as the debate is about Harris and Trump, the running mates got here in no small part because of their respective biographies.

Trump’s choice was a play to further cement the GOP ticket as the choice for middle America. The author of the “Hillbilly Elegy” memoir who grew up in small-town Ohio, Vance has roots to match his economic populism in ways the billionaire Trump does not.

Walz and Harris both grew up middle class, but Walz remains firmly ensconced there, going from his boyhood on a Nebraska farm to the high school classrooms of Minnesota before he ran for office. It’s both a juxtaposition with and reinforcement of Harris’ story as the daughter of an Indian mother and Jamaican father.

Both men have made their families part of their political identities. Each have working spouses. Walz has two children — young adult and teenage. Vance has three young sons. The Walzes and Vances are more traditional political families than those of the presidential nominees: Harris has adult stepchildren from her decade-old marriage to Doug Emhoff; Trump has five children from three marriages.

Expect both running mates, even as they try to keep the spotlight on their bosses, to highlight their own stories.

The fact-checking onus will be on the candidates

CBS announced Friday that it will be up to the candidates to keep each other honest at Tuesday’s debate — a sticking point from earlier debates this year.

In the June debate between Trump and Biden, CNN’s Jake Tapper and Dana Bash limited follow-up questions and did not fact check either participant. In the September debate between Trump and Harris, ABC’s David Muir and Linsey Davis interjected with matter-of-fact corrections to some of Trump’s most glaring misstatements.

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Associated Press writer Mary Clare Jalonick in Washington contributed to this report.