Vice presidential debates rarely — if ever — alter the course of an election. Case in point: The most memorable moment of 2020's clash between Republican Mike Pence and Democrat Kamala Harris was when a fly landed on Pence's head.

This year's edition, however, could exceed expectations. For one thing, the meeting tonight between Ohio Sen. JD Vance and Minnesota Gov. Tim Walz will likely be the final debate of 2024. Typically, the presidential candidates face off one or two more times after their running mates go at it. But because former President Donald Trump has refused to debate Harris again, tonight may be the last best chance for either ticket to connect with a national audience before Election Day.

Then there’s the unusual symmetry between Walz and Vance to consider. Both are white Midwestern guys with military experience, and both focus on the economic well-being of the people they grew up with. Yet their policy prescriptions couldn’t be more different. Tonight's debate will test whether Harris or Trump has picked the superior middle-class messenger — a choice that could, in turn, affect how Rust Belt battlegrounds like Michigan, Wisconsin and Pennsylvania vote on Nov. 5.

So what do Walz and Vance need to accomplish in New York City? Here’s a quick Yahoo News guide.

What Walz needs to accomplish

Sell Harris as the 'normal' choice. Walz might be the "weird" guy — that is, the pol who popularized the Democrats' new favorite description of Trump, Vance and their fellow MAGA Republicans. But since joining the ticket, the Minnesotan's mission has been to seem as "not weird" as possible — and to help Harris's Democratic Party seem more mainstream than Trump's GOP in the process.

That will be Walz’s main objective tonight as well: to validate his running mate and give undecided voters “permission” to break her way.

After all, it isn't hard to imagine a world in which Harris — the biracial daughter of immigrant parents who met in a Black nationalist study group at Berkeley in the 1960s — is cast as too unconventional for the presidency. She would be the first woman president, the first Indian-American president and the first Black woman president. She even hails from San Francisco.

In contrast, Walz reads like a "typical Trump supporter" — at least on paper. As his wife, Gwen, said in an introductory video at the Democratic National Convention in August, he "grew up in a small town in Nebraska … spent summers working on the family farm …. went to college on the G.I. Bill … taught for over 15 years … coached football and led the team to a state championship … spent a lot of time working with Republicans [in Congress] … [and is a] lifelong hunter and gun owner." He also served in the Army National Guard, drives a vintage truck, wears flannels and a camo cap and listens to Bob Seger.

Tonight, Walz will talk about the things he's done: advising his school's gay-straight alliance; enduring fertility treatments; supporting background checks and red-flag laws; passing a flurry of progressive policies as Minnesota governor, including paid family leave and free school lunch. He will talk about the things he and Harris want to do if elected. And throughout, his implicit argument will be that these are the sort of things a guy like him — a guy who might otherwise vote for Trump — can get behind.

Keep Vance on defense. On the other hand, Walz likes to claim that Trump and Vance are pushing policies that "nobody asked for."

“It’s an agenda that serves nobody except the richest and the most extreme among us — and it’s an agenda that does nothing for our neighbors in need,” he said at the convention. “Is it weird? Absolutely. But it’s also wrong, and it’s dangerous.”

The strategy here is to "other" Trump-Vance before Trump-Vance can other Harris-Walz — and so far, it's been moderately successful. Vance in particular has suffered since Walz entered the race. Over the last month, Vance's favorable rating has fallen to 31%, according to the latest Yahoo News/YouGov poll — the lowest of any of the presidential or vice presidential candidates. The Ohioan's unfavorable rating has risen to 48% as well, putting him "underwater" by 17 percentage points — again, the worst of the bunch. Meanwhile, Walz is seen more favorably (39%) than unfavorably (37%).

Much of the problem is that Vance has spent recent weeks playing defense: for criticizing Harris and others as "childless cat ladies" who don't have a stake in the future of the country; for claiming that Trump would veto a national abortion ban when Trump has said no such thing; for insisting that Haitian migrants in Springfield, Ohio, are eating their neighbor's cats and dogs long after such rumors were debunked.

"If I have to create stories so that the American media actually pays attention to the suffering of the American people," Vance said in reference to the pet-eating lies, "then that's what I'm going to do."

The more Walz can play the attack dog tonight — the more he can force Vance to play defense — the better it is for Democrats. As the old political saying goes, "If you're explaining, you're losing."

Put 'honesty' attacks to bed. In all likelihood, Walz will also spend some time explaining himself during the debate. Vance is almost certain to claim — as he's done on the campaign trail — that his Democratic counterpart has misrepresented his military record and his family's fertility struggles (if the moderators don't go there first). And Walz will have to respond.

The fertility flap is fairly simple. In an early campaign email, Walz’s team shared an article that referenced “his family’s IVF journey” in order to draw attention to conservative challenges to the procedure; Walz went on to claim that “If it was up to [Vance], I wouldn’t have a family because of IVF.”

But Gwen Walz soon clarified that she and her husband had conceived their daughter via intrauterine insemination (IUI) rather than in-vitro fertilization. While IUI is a fertility treatment often attempted before IVF, it has not been challenged in court because it doesn’t risk destroying unused embryos.

In response, Vance called Walz a liar. "Today it came out that Tim Walz had lied about having a family via IVF," he wrote on social media. "Who lies about something like that?"

The military back-and-forth is a little more convoluted; it involves Vance accusing Walz of “stolen valor” for implying he’d served in a combat zone during his 24 years with the Army National Guard and for retiring before his unit deployed to Iraq.

Those around Walz — including his wife and his staffers — have responded to these accusations already, saying he "misspoke" when he mentioned "carrying weapons in war" and that he was "using commonly understood shorthand for fertility treatments" when he referenced IVF.

But Walz himself hasn’t addressed them directly. Tonight, he’ll be aiming to deliver quick, clear explanations meant to squelch the sort of “exaggerator” claims that plagued his Democratic predecessors Al Gore and John Kerry — and preserve the credibility required to vouch for his running mate.

What Vance needs to accomplish

More Harris, less Vance. For the first few months of his vice presidential candidacy, Vance has gotten far less attention for attacking his opponents than for defending himself (see above). Tonight's debate offers him a chance to change that unhelpful trajectory.

Of course, Trump hardly needs an traditional “attack dog” sidekick; he relishes going after rivals himself. But voters tend to tune out lines they’ve heard a million times before, and Trump tends to repeat himself.

Tonight, Walz and the moderators will try to make Vance answer for his running mate's excesses, his own controversial comments and his past criticismsof Trump. His goal should be to pivot to offense — on Walz's credibility; on how Walz responded to the George Floyd riots in Minnesota; on Harris's border record — as quickly as possible, and to frame his criticisms in fresh ways that connect with average Americans rather than the extremely online right.

So far, Vance — who is extremely online himself — has struggled to pull this off. It would be wise for him to hit reset at the debate. Why? Because the extremely online right is already voting for Trump, who has been stuck at 45% in the national polls for months. To win, Vance and his boss will have to reach voters who don't think Haitian migrants eat pets.

Flesh out Trump's agenda. Walz's strategy on policy will be similar to his boss's: tie Vance and Trump to Project 2025, a 922-page blueprint to radically reshape the U.S. government that was created for the next Republican administration by the Heritage Foundation and other conservative groups.

Despite the fact that at least 25 of Project 2025's 36 listed authors and editors have served Trump in some capacity — and despite Vance's own links to its architects — the GOP ticket has repeatedly distanced itself from the controversial document.

"I have no idea who is behind it," Trump wrote on social media in early July. "I disagree with some of the things they're saying and some of the things they're saying are absolutely ridiculous and abysmal. Anything they do, I wish them luck, but I have nothing to do with them."

But if not Project 2025, then what? Since Trump rarely addresses policy specifics, the onus will be on Vance to flesh out the former president’s second-term agenda. How exactly do Trump and Vance intend to “commit to the working man,” to “fight for American citizens” and to “stamp more and more products with that beautiful label ‘Made in the USA,’” as the senator put it at the Republican National Convention in July?

With immense tariffs on foreign — especially Chinese — goods? By deporting millions of undocumented immigrants? By exerting more control over the Federal Reserve? A new working paper released Thursday by the Peterson Institute for International Economics says those policies would weaken growth, increase inflation and reduce employment — potentially through 2040. What else does Trump's "new American industrialism" involve? And why does Vance think it will help the working man? Tonight is his opportunity to make the case.

Look to the future. Vance, 40, would be the youngest veep since Richard Nixon. Articulate and wonky, he is widely seen as a "next generation" leader of Trump's MAGA movement.

"The Ohio Senator has positioned himself at the vanguard of an emerging ideology often described as the 'New Right' or 'National Conservatism,'" as a new cover story in Time magazine puts it — a socially conservative, economically populist "political project [that] aims to resolve a long-­standing issue for Republicans, whose need to win over heartland voters on cultural issues is in tension with an economic agenda that has benefited the wealthy over the working class."

Vance’s explicit objective tonight is to help Trump get elected in November. But his implicit objective — as it is with most vice-presidential nominees — is to position himself for whatever comes next.

"Trump will, at most, serve four years in the White House," Vance has said. "There is a big question about what comes after him."

A strong performance could help the senator erase some of his early stumbles on the national stage and position him as a future party leader, regardless of who wins in November. A weak debate will likely have Republicans looking elsewhere.