WASHINGTON (AP) — Tim Walz and JD Vance will meet for their first and possibly only vice presidential debate Tuesday, in what could be the last debate for both campaigns to argue their case before the election.

The debate in New York hosted by CBS News will give Vance, a Republican freshman senator from Ohio, and Walz, a two-term Democratic governor of Minnesota, the chance to introduce themselves, make the case for their running mates, and go on the attack against the opposing ticket.

Tuesday's matchup could have an outsized impact. Polls have shown Vice President Kamala Harris and former President Donald Trump locked in a close contest, giving added weight to anything that can sway voters on the margins, including the impression left by the vice presidential candidates. It also might be the last debate of the campaign, with the Harris and Trump teams failing to agree on another meeting.

The role of a presidential running mate is typically to serve as an attack dog for the person at the top of the ticket, arguing against the opposing presidential candidate and their proxy on stage. Both Vance and Walz have embraced that role.

Vance's occasionally confrontational news interviews and appearances on the campaign trail have underscored why Trump picked him for the Republican ticket despite his past biting criticisms of the former president, including once suggesting Trump would be “America’s Hitler.”

Walz, meanwhile, catapulted onto Harris’ campaign by branding Trump and Republicans as “ just weird,” creating an attack line for Democrats seeking to argue Republicans are disconnected from the American people.

A new AP-NORC poll found that Walz is better liked than Vance, potentially giving the Republican an added challenge.

After a Harris-Trump debate in which Republicans complained about the ABC News moderators fact-checking Trump, Tuesday's debate will not feature any corrections from the hosts. CBS News said the onus for pointing out misstatements will be on the candidates, with moderators “facilitating those opportunities.”

Both sides are trying to lower expectations

Ahead of the debate, allies of both men were lowering expectations that their candidate will have a decisive performance.

Sen. Amy Klobuchar, D-Minn., called Vance “an accomplished debater” and contrasted that with Walz, saying he was “not a lawyer-debater type.” Klobuchar said Walz spent time growing up thinking about football, not debating.

Jason Miller, a senior adviser to Trump, portrayed Walz much differently than Klobuchar.

“Tim Walz is very good in debates, really good. He’s been a politician for nearly 20 years. He’ll be very well prepared for tomorrow night,” Miller told reporters Monday. He predicted the Democratic governor of Minnesota will be much more “buttoned up” than he is on the campaign trail and ready to defend his record, but added, “That’s not to say that JD Vance won’t be prepared tomorrow, or that somehow he isn’t up to the challenge.”

Vance, speaking to reporters last week, said he didn’t “have to prepare that much” for the debate because he had “well-developed views on public policy.”

But Vance has been doing debate prep sessions where he’s been joined by his wife, Usha Vance, Miller, senior Vance aides, and Rep. Tom Emmer, R-Minn., who has played Walz, according to a person familiar with his preparations who requested anonymity to discuss strategy. Moderating their mock debates was Monica Crowley, who served in the Trump administration, hosts a podcast and contributed to Project 2025, a conservative blueprint for remaking government that Trump claims he knows " nothing about.”

“JD Vance is prepared to wipe the floor with Tim Walz and expose him for the radical liberal he is,” Emmer told reporters on Monday.

Walz’s debate prep has included sessions hunkered down in a Minneapolis hotel, with Transportation Secretary Pete Buttigieg standing in for Vance, according to a person familiar with the process who requested anonymity to discuss the campaign's internal dynamics. Others helping in the preparations include Rob Friedlander and Zayn Siddique, who helped Harris prepare for her debate with Trump, along with other aides to Walz and the campaign.

Klobuchar said Walz will show the American people “a real person” who brings “buoyancy” and positivity to the debate stage that will contrast with Vance, but “he is not going to be shy about pointing out the problems.”

“Just because he’s an optimistic, positive person doesn’t mean he’s a pushover,” she said.

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Associated Press writers Jill Colvin in New York, Josh Boak in Baltimore, and Meg Kinnard in Columbia, South Carolina, contributed to this report.