Do vice-presidential debates matter? Conventional wisdom says no. Historically, polls have shown that those quadrennial 90 minutes have little effect on how people will vote in the presidential election.

Tuesday night’s debate between the Democratic nominee, Minnesota Gov. Tim Walz, and his Republican opponent, Sen. JD Vance of Ohio, seems to be following that pattern. Some pundits have claimed that Vance, who delivered a polished and unflappable performance, “won” the debate; Walz appeared more nervous and fumbled several questions, although he did, according to fact-checkers, lie far less often. Walz also scored big at the end, when he pushed Vance to confirm that President Biden did win the 2020 election and called Vance‘s deflection “a damning nonanswer.”

According to instant post-debate polling, most voters considered the debate a tie, and both men saw bumps in their favorability ratings, although these are unlikely to change that fact that Walz’s numbers are unusually high while Vance’s are remarkably low.

None of which, as previously stated, will likely matter come November.

Except for one thing. One very important and rarely mentioned thing: If Donald Trump wins, Vance could very well become president. Which should be a concern considering how historically low Vance’s approval ratings are: Before the debate, Vance was more unpopular than any vice-presidential pick in modern history, including Sarah Palin, who is often credited with helping John McCain lose his election in 2008.

Vance would be, after all, a heartbeat away from the presidency. And should he win, the 78-year-old Trump would, by the end of his term, become the oldest president ever to hold the office.

And Trump’s recent rambling and nonsensical speeches, as well as his decision to refuse a second debate with his Democratic rival, Vice President Kamala Harris, and pull out of a scheduled “60 Minutes” interview, indicate that he may already be struggling with issues of cognition and/or stamina, in addition to whatever strategic reasons are behind the choices.

In addition to regular non sequiturs about sharks and Hannibal Lecter, and outrageous lies that Haitian immigrants in Springfield, Ohio, are eating their neighbors’ dogs and cats, Trump recently accused the president of North Korea of trying to kill him (he appears to have confused North Korea with Iran) and acknowledged that he doesn’t know what the Congo is (even as he falsely claimed that “many people” from there are flooding the U.S.)

It goes without saying that if Harris said any of these things, the press would be calling on her to step down. Which is precisely what happened after President Biden fumbled, in a far less dramatic way, his June debate against Trump.

In the absence of Biden on the campaign trail, Trump and Vance have been attacking Harris’ “policies,” which honestly displays a shocking ignorance about the role of vice president.

Those of us who have taken a high-school civics class, or seen at least one episode of “The West Wing” or “Veep,” understand that the main function of the vice president is to support the president, occasionally fill in for the president and, most important, assume the office of the presidency should the president die or become incapacitated.

Even if Trump’s notable lack of coherence and energy are not indications of mental and physical decline, the fact remains that Vance is, based on Trump’s age alone, among the vice-presidential candidates most likely to be called upon to fulfill that role in the history of the republic.

Yes, the guy who wrote the intro to Project 2025, who doesn’t trust people that don’t have children, who admitted that the racist tales about the Haitian community in Springfield were false but spread them anyway, who thinks that women should stay in abusive relationships for the sake of “family” and that the solution to our childcare problem is Grandma and who has referred to rape as an “inconvenience.” That guy could very well become our president.

So Tuesday night’s debate should be seen less as Vance facing off with Walz and more as Vance offering a preview of himself as leader of the free world.

As many have said in praising his performance, Vance offered a more polished version of Trump’s many ill-considered policies (tariffs, Project 2025), mischaracterizations (say, about the Biden administration’s responsibility for inflation) and outright lies (claiming that violent crime is up, for instance, or that most Americans support draconian abortion laws.)

Most important, by refusing to contradict Trump’s Big Lie about the 2020 election, Vance told us pretty much all we needed to know about his potential presidency. As an undecided Michigan voter told CNN after the debate: “I don’t think I can trust someone with my vote if they’re not going to respect it.”

When Biden defeated Trump in 2020, many worried that MAGA Republicans would next find a candidate who would push the same nationalistic, elitist and divisive agenda, only without the orange makeup, the many lawsuits and the tendency to veer off into narcissistic and often baffling rants.

Based on the vice-presidential debate, it looks like they have.