When Donald Trump and Kamala Harris meet onstage Tuesday night in Philadelphia, they’ll both know there’s little debate that Pennsylvania is critical to their chances of winning the presidency.

The most populous presidential swing state has sided with the winner of the past two elections, each time by just tens of thousands of votes. Polling this year suggests Pennsylvania will be close once more in November.

A loss in the state will make it difficult to make up the electoral votes elsewhere to win the presidency. Trump and Harris have been frequent visitors in recent days — Harris plans to return on Friday — and the former president was speaking in Butler County on July 14 when he was the target of an assassination attempt.

The stakes may be especially high for Harris: No Democrat has won the White House without Pennsylvania since 1948.

Pennsylvanians broke a string of six Democratic victories in the state when they helped propel Trump to victory in 2016, then backed native son Joe Biden in the 2020 race against Trump.

“They say that ‘If you win Pennsylvania, you’re going to win the whole thing,’” Trump told a crowd in Wilkes-Barre’s Mohegan Arena in August.

Republicans are looking to blunt Trump’s unpopularity in Pennsylvania’s growing and increasingly liberal suburbs by criticizing the Biden administration's handling of the economy. They hope to counter the Democrats’ massive advantage in early voting by encouraging their base to vote by mail.

Harris is looking to reassemble the coalition behind Biden's winning campaign, including college students, Black voters and women animated by protecting abortion rights.

Democrats also say it will be critical for Harris to win big in Philadelphia — the state's largest city, where Black residents are the largest group by race — and its suburbs, while paring Trump's large margins among white voters across wide swaths of rural and small-town Pennsylvania.

The debate is set for the National Constitution Center in Philadelphia. The city is a Democratic stronghold where Trump in 2020 notoriously said “ bad things happen,” one of his baseless broadsides suggesting that Democrats could only win Pennsylvania by cheating.

Biden flipped Pennsylvania in 2020 not just by winning big in Philadelphia, but by running up bigger margins in the heavily populated suburbs around Philadelphia and Pittsburgh. He also got a boost in northeastern Pennsylvania in the counties around Scranton, where he grew up.

Ed Rendell, a former two-term Democratic governor who was hugely popular in Philadelphia and its suburbs, says Harris can do better than Biden in the suburbs.

“There’s plenty of votes to get, a Democrat can get a greater margin in those counties,” Rendell said.

Lawrence Tabas, chair of Pennsylvania’s Republican Party, said Trump can make gains there, too. The GOP’s polling and outreach shows that the effect of inflation on the economy is a priority for those suburbanites, he said, and that the issue works in the party's favor.

“A lot of people are really now starting to say, ‘Look, personalities aside, they are what they are, but we really need the American economy to become strong again,’” Tabas said.

Rendell dismisses that claim. He said Trump is veering off script and saying bizarre things that will ensure he gets a smaller share of independents and Republicans in the suburbs than he did in 2020.

“He’s gotten so weird that he’ll lose a lot of votes," Rendell said.

Harris has championed various steps to fight inflation, including capping the cost of prescription drugs, helping families afford child care, lowering the cost of groceries and offering incentives to encourage home ownership.

Pennsylvania’s relatively stagnant economy usually lags the national economy, but its unemployment rate in July was nearly a full percentage point lower. The state's private sector wage growth, however, has slightly lagged behind the nation’s since Biden took office in 2021, according to federal data.

Meanwhile, Democrats are hoping the enthusiasm since Biden withdrew from the race and Harris stepped in will carry through Election Day in November.

For one, they hope she will do better with women and Black voters, as the first female presidential nominee of Black heritage. Rendell said he is more optimistic about Harris' chances to win Pennsylvania than he was with Biden in the race.

"I think we're the favorite now," Rendell said.

The debate takes place before voting starts — in Pennsylvania and everywhere else.

A national Associated Press-NORC Center for Public Affairs Research survey conducted in July showed that about 8 in 10 Democrats said they would be satisfied with Harris as the party’s nominee compared with 4 in 10 Democrats in March saying they would be satisfied with Biden as the candidate.

There is some optimism among Pennsylvania Democrats even in Republican-leaning counties, including a number of whiter, less affluent counties near Pittsburgh and Scranton that once voted for Democrats consistently.

In Washington County, just outside Pittsburgh in the heart of the state's natural gas-producing region, Larry Maggi, a Democratic county commissioner, thinks she will outrun Biden there.

Maggi is seeing more lawn signs for Harris than he ever saw for Biden, as well as more volunteers, many of whom are young women concerned about protecting abortion rights.

“I’ve been doing this for 25 years and I’m seeing people I’ve never seen,” Maggi said.

Democrats also hope there is a growing number of voters like Ray Robbins, a retired FBI agent and registered independent, who regrets voting for Trump in 2016. Robbins did so, he said, because he thought a businessperson could break congressional deadlock.

“He’s a liar,” Robbins said. “I think he’s totally devoid of any morals whatsoever. And you can quote me: I think he’s a despicable human being even though I voted for him.”

But Republicans have reason to be optimistic, too.

In the nation's No. 2 gas-producing state, even Democrats acknowledge that Harris' prior support for a fracking ban in her run for the 2020 nomination could prove costly. In this campaign, the vice president said the nation can achieve its clean energy goals without a ban, though Trump insists she will reverse course again.

Meanwhile, the Democratic advantage in the state's voter registration rolls has steadily shrunk since 2008, from 1.2 million to about 350,000 now.

Republicans credit their outreach to younger voters, as well as Black, Asian and Hispanic voters.

“A lot of them tell us it’s the economy," Tabas said. “And in Philly, it's also the crime and safety in the neighborhoods and communities.”

Those gains have yet to translate into GOP wins as Democrats have beaten Republicans by more than 2-to-1 in statewide contests the past decade.

Daniel Hopkins, a political science professor at the University of Pennsylvania, chalks up the narrowing registration gap, in part, to “Reagan Democrats” who have long voted for Republicans, but did not change their registration right away.

One of those voters is Larry Mitko, a longtime Democrat-turned-Republican who lives in a Pittsburgh suburb.

Mitko, 74, voted for Trump in 2016 and Biden in 2020, and was leaning toward voting for Trump in 2024 because of inflation and Biden's handling of the economy before Biden exited the race.

That is when Mitko became sure he would vote for Trump.

“I don’t like the fact of how they lied to us telling us, ‘He’s OK, he’s OK,’ and he can’t walk up the steps, he can’t finish a sentence without forgetting what he’s talking about,” Mitko said of Biden.

Harris’ late entry into the race could mean that many voters are still learning about her, said Kathleen Hall Jamieson, a University of Pennsylvania professor of communication who researches presidential debates.

More voters than usual may not be locked into a decision even as voting looms, Jamieson said, so this debate could make a difference.