When Republican vice-presidential candidate JD Vance takes the debate stage Tuesday, it may be the first time millions of Americans hear directly from the senator from Ohio. But one person in particular could be his most important viewer: his running mate, Donald Trump.

Trump, a former pitchman, voracious television watcher and skilled showman, is known to focus intensely on television performances, and his appreciation of Vance’s forceful defenses of him in interviews played a significant role in his selection as the No. 2. As Vance prepares to face Minnesota Gov. Tim Walz, strategists expect he will reprise the combative posture he has taken on the campaign trail.

“Trump likes that he’s able to go into the lion’s den and communicate on policy issues,” said one person familiar with Vance’s debate preparations, speaking on the condition of anonymity to describe internal strategy. “That’s probably going to be a big scene that will please him.” Vance’s aides say privately that his experience facing skeptical interviewers could help him at Tuesday’s debate.

Walz, the Democrats’ vice-presidential pick, faces a different challenge Tuesday. A little-known governor until a few weeks ago, he is not a best-selling author or high-profile senator like Vance, and he faces the task of introducing himself to millions of Americans who may have little sense of his record or what he stands for.

Vice-presidential debates often have a limited effect, if any, on the outcome of a presidential contest, because by definition they involve secondary figures. But strategists on both sides say this time may be different, because Trump and Harris are on course to have just one debate and it has already happened, meaning Tuesday will be the last faceoff between the two tickets before many voters cast their ballots.

“It seems to be that there will not be another presidential debate, so this will be the last opportunity, very likely, that the American electorate will have the chance to see two different candidates on the same stage talking about the different visions that they have,” said longtime Trump adviser Corey Lewandowski.

Vance has attracted unusual attention for some of his incendiary comments, such as previously calling prominent female Democrats “a bunch of childless cat ladies who are miserable” and his more recent amplification of the false claim that Haitian immigrants are eating their neighbors’ pets. Vance is almost certain to be face questions about those comments on Tuesday.

In addition, Trump, at 78, would be the oldest president in history at the end of his term if elected. Polls suggest Americans are less worried about his age than they were about that of President Joe Biden, who is 81. But the issue nonetheless shines an additional spotlight on Vance’s readiness to step into the Oval Office.

Matt Gorman, a Republican strategist who most recently worked on the presidential bid of Sen. Tim Scott (R-S.C.), said Vance will benefit from having regularly faced questions from reporters.

“Among the best debate prep you can do is do interviews, so Vance has been doing that,” Gorman said. “He’s the king of the Sunday shows. That will help him.”

Gorman said that has helped Vance become adept at avoiding “rabbit holes.” Analysts on both sides said after the Trump-Harris debate on Sept. 10 that Trump had failed to avoid such traps, often taking the bait when Harris raised subjects he was sensitive about.

Walz, for his part, started to prepare for the debate several weeks ago, meeting with aides in Minneapolis and on the road. In recent days, he has participated in a more intensive “debate camp” in Harbor Springs, Mich., where aides constructed a mock debate studio and Pete Buttigieg, the transportation secretary, has played Vance in mock sessions. (Buttigieg did this in his private capacity.)

The debate has been a source of anxiety for Walz, according to people close to him, who spoke on the condition of anonymity to discuss his private mood. Walz conceded to Harris when she was evaluating him as a potential running mate that he was not an experienced debater, the people said, adding that he is concerned about letting the campaign down on Tuesday night.

Asked shortly after the Harris-Trump debate whether he had started thinking about his own meeting with Vance, Walz said he had. “Yes, I need to,” he told MSNBC. “Look, he’s Yale Law guy. I’m a public school teacher. So we know where he’s at on that.”

Some Democrats, however, are less concerned, noting that polls suggest Walz is far more popular than Vance. They predicted he would spend much of his time onstage criticizing Trump rather than going after Vance.

Walz probably will be forced to defend not only his record — including his military service, his handling of racial justice protests as governor and his liberal policy positions — but also Harris’s record, as Vance is set to paint her as an out-of-touch California liberal.

Lewandowski said Vance’s rise from a hardscrabble childhood to Yale Law School to the U.S. Senate by age 38 illustrates his intelligence. Another campaign official, speaking on the condition of anonymity to describe internal discussions, said Trump wants Vance to show his “smarts” on Tuesday.

Vance’s team has also been preparing their candidate for weeks, with help from Rep. Tom Emmer (R-Minn.), who has been playing the part of Walz in mock debate sessions. Aides have also been studying Walz’s debate performances in his gubernatorial and congressional races, according to one of the people familiar with the debate prep.

Vance’s team expects Walz to depict Vance as an extremist and tie him to Project 2025, an agenda for a future Republican administration assembled by the Heritage Foundation. Trump has sought to distance himself from the document, although many former Trump administration officials helped write it.

Vance’s aides also view Walz as scripted, and they are hoping to draw him away from prepared talking points. When Vance debated then-Rep. Tim Ryan (D-Ohio) during their U.S. Senate race, Vance at one point responded to a Ryan quip by alleging, “Consultants gave you this line.”

But Walz will have his own ammunition to use against his Republican opponent. Before he ran for Senate, Vance had a long history of criticizing Trump, at one point referring to himself as “a ‘Never Trump’ guy.” Vance has said that he came around once he saw Trump’s economic success in office.

Still, that history has put an unusual spotlight on the relationship between the Republican nominee and his running mate, and many Republicans will be watching closely to see how Vance responds when that is raised. Vance, as if to dispel any notion of tension, frequently jokes in campaign speeches that Trump has not let him live down his past remarks. He also mentions that he often speaks to Trump by phone, recently describing how the former president called him after facing an assassination attempt.

Also looming over Vance is Trump’s history with his last vice president, Mike Pence. Pence was a deeply loyal second-in-command, but he earned Trump’s wrath by not interfering with Congress’s certification of Biden as the victor in the 2020 election, a race that Biden had rightfully won.

Marc Short, Pence’s longtime chief of staff, said he expects Vance to have little problem getting across the points Trump wants to hear Tuesday night, given his pedigree and speaking ability.

Trump did not interfere in Pence’s debate preparations in 2016 or 2020, he said. “Much has been written about the relationship today, but the relationship was pretty close then,” Short said of Trump and Pence. “Trump entrusted Pence entirely to know how to prepare for it and do it the way he wanted.”

Standing toward the back of Trump’s town hall Friday in Warren, Mich., Rick Lynn, 75, said Vance has said everything he wants to hear on immigration, the economy and more. Although he is a Trump supporter, Lynn said he worries that Trump will fail to appreciate Vance.

“With Donald Trump, you never know what he wants from anyone,” the Trump voter said. “He’s probably going to treat Vance like he did Pence — take him for granted.”