Kamala Harris and Donald Trump are preparing for their first debate in Philly. Here's what's at stake.

PHILADELPHIA — The spotlight aimed at Pennsylvania is going to need a new bulb soon.

Tuesday's debate between former President Donald Trump and Vice President Kamala Harris at 9 p.m. at the National Constitution Center will become the latest high-stakes moment in an unprecedented presidential campaign playing out in Pennsylvania.

The impact could be huge. The race is essentially tied in Pennsylvania, which could determine the whole election — and while polling shows that Harris has made up ground from where President Joe Biden was, she's far from definitively overcoming Trump, who still enjoys substantial support in the state.

Debates can be consequential, as this election season has already shown. And Tuesday could wind up being the only debate between Harris and Trump before the November election.

So what do both candidates have to do, and what are we watching for?

Trump allies hope he keeps his cool, focuses on issues

Trump comes in with an advantage of experience, as this will be his seventh general election debate — more than any other candidate in history. His team also won the war over muting the candidates' mics when they're not speaking, which means he'll have less leeway to interrupt or go on tangents.

His allies want him to stick to the issues, particularly immigration and inflation, and to tie Harris to Biden on both. He'll also likely try to argue Harris, who is less well-known than the presidential candidates before her, is not yet ready to run the country. It's all an opportunity to slow some of the momentum Harris enjoyed coming out of the Democratic National Convention.

"[Harris] told the world on CNN 'my values have not changed,' so we're going to pin her actual record to her," Trump senior adviser Tim Murtaugh said, previewing an attack on Harris over issues she's pivoted on, like fracking. "Her record is what it is... She is a San Francisco liberal who is pretending not to be one and she will not be allowed to get away with that."

Murtaugh said Trump will also emphasize Harris is part of the Biden-Harris administration Harris and Trump are readying for their first debate in Philly. Here's what's at stake. "She cannot run as an outsider."

Calm and disciplined aren't typically words used to describe Trump on stage, RNC chairman Andy Reilly acknowledged. But he said it's the former president's best chance at capturing undecided voters, a small but potentially crucial group in neck-and-neck swing states like Pennsylvania.

"Sure, there will be times Trump goes off message and can't help himself. I tell him, [when it comes to] persuadable voters, that's not gonna ring the bell for them."

Harris looks to further define herself and let Trump be Trump

Harris, who will conduct her debate prep from — where else? — Pennsylvania, will look to hammer Trump on issues like reproductive rights and threats to democracy while laying out her priorities. It will be the first time the two have shared a room since Trump's State of the Union addresses when Harris was a senator, and comes after Trump has unleashed racist and sexist attacks on her.

Thus far, Harris has established herself as above the often racist and sexist accusations he's wielded at her, rarely engaging in any response — and that strategy may continue on the debate stage on Tuesday. There's also the question of whether Trump will further alienate himself from some voters by doubling down on those attacks on stage.

Eric Stern, a Democratic strategist in Pennsylvania, said Harris' best move is to "let Trump dig himself into a hole."

"He has a unique talent to do that."

Stern thinks that's an achievable mission for Harris, even in a format without muted mics, which could restrain Trump somewhat. "She should let him take his full 60 — and then 30 and whatever — to tell us all what he really thinks," Stern said.

Both will be making their pitch to a very small group of undecided voters

Even after Harris replaced Biden as the Democratic nominee, voters expressed frustration with the political system — a sentiment that's often especially true for undecided voters, who tend to be moderate or independent.

While both Trump and Harris have served in the White House, they have each tried to present themselves as the candidate who can bring a fresh start. Some of Trump's campaign signs read "Let's Save America." Harris has been vice president for nearly a term, but frequently talks to voters about "fighting for a brighter future." As both candidates make a pitch that they're the change the country needs, who will do it more effectively?

"He has to remember that his target audience is a swing persuadable voter," Reilly said. "This is when the swing voter is focusing in on the race and he has to debunk the Kamala 2.0 movement for them. He needs to remind people, with facts in a calm way, that Harris was there. Harris had a long record prior to being the vice president and as vice president, she supported views of Biden's which have turned them off."

For Harris' part, Stern thinks she needs to tell voters about the specifics of her plans and how they can help working-class Americans, a key voting bloc in Pennsylvania and other "Blue Wall" states.

"I'm excited for her to talk about abortion rights and greedflation and going after corporate price gouging," he said.

Ultimately, he thinks her best appeal to undecided voters who may be watching is an anti-Trump pitch.

"Tell them, this guy is a crook, this guy is dangerous. He has been convicted of crimes ... he will not be good for you, he is dangerous."

Look for questions about fracking, U.S. Steel, and other direct appeals to Pennsylvania

The two candidates are bound to cover a lot, but with the debate taking place in Pennsylvania — the state both Trump and Harris see as a pathway to the presidency — look for appeals on two very commonwealth-specific issues: Fracking and the sale of Pittsburgh's U.S. Steel.

"I think you might hear a thing or two about fracking," Murtaugh, the Trump campaign adviser and a Pennsylvania native, said.

Ironically, they're also both issues Harris and Trump agree on now. But on both, Harris has only recently solidified her stance, saying she won't ban fracking and also opposes the sale of U.S. Steel to Japan.

Look for Trump to try to argue he's the legitimate champion of the Rust Belt, and for Harris to double down on her positions.