“We are the Keystone State,” said Pennsylvania Democratic Attorney General Josh Shapiro. “It’s clear from an Electoral College perspective, if you look at the map from last cycle, just how pivotal Pennsylvania is. At the end of the day, I think if Pennsylvania goes, so will go the country.”

Biden is beating Trump by 4 or 5 percentage points here, according to polling averages — a decent but not overwhelming lead that is within some surveys' margin of error. Pennsylvania and its 20 Electoral College votes have more psychological significance to Biden’s campaign than any other state. Biden’s political persona is rooted in his childhood in Scranton, his campaign was headquartered in Philadelphia until the pandemic began, and he has held more events in Pennsylvania than any other battleground.

Similar to Pennsylvania for Biden, Florida has been Trump’s obsession since he won it in an upset in 2016 and subsequently changed his residence to the state. No Republican in almost a century has won the White House without Florida, which now has 29 electoral votes.

Most polls in Florida show Trump losing to Biden, albeit within the margin of error and by a smaller amount than in Pennsylvania. But Trump’s campaign said it feels confident in Florida, in great part because GOP turnout of high-propensity voters has been so high during early voting.

“What we have left on the table vs. what they have left on the table looks better for us,” said Marc Reichelderfer, a top GOP consultant in Tallahassee.

If Florida and the other Sun Belt swing states he won in 2016 are secured, however, Trump still needs one more big win up north. Pennsylvania looks like the place to do it, according to the campaign’s polling and public surveys that show it closer than Wisconsin or Michigan.

Pennsylvania is also the most likely tipping-point state, and there are more votes left on the field here: Fewer 2016 voters in Pennsylvania have turned out during early voting than in the other Rust Belt states.

“Pennsylvania will determine whether the president wins again,” said former Pennsylvania Rep. Lou Barletta, a top Trump ally here. “I believe it can be that close.”

Though Biden’s campaign is bullish about his position here, his staff won’t go as far as to say that it is a must-win state for the former vice president. His aides believe that he benefits from an Electoral College map where there are multiple avenues to victory.

“Going into these last few days, we still have a number of paths to 270 on election night,” said Molly Ritner, Biden’s deputy states director. While the campaign doesn’t believe it needs to, she added, “We can win without Pennsylvania.”

But Pennsylvania is critical to Biden’s team for another reason. Referring to Trump, Becca Siegel, Biden’s chief analytics officer, said, “I think that if he doesn’t win Pennsylvania, that leaves very, very few options for how he wins this election.”

A key element of Trump’s strategy in Pennsylvania is to boost turnout in the southwestern part of the state, home to much of the state’s natural gas industry, where the president ran up the score four years ago. Biden’s slip-up in the final debate over fossil fuels left Republicans thinking he looked vulnerable to Trump. On Saturday, Trump held a massive rally in Butler County that was so packed that it left some Democrats rattled about the possibility of a 2016 repeat.

“It’s hard not to look at this crowd that Trump assembled in Butler, PA and not be completely terrified that he could win again,” tweeted Rebecca Katz, a progressive strategist who worked for Pennsylvania Lt. Gov. John Fetterman during his 2018 campaign.

Another place that Trump’s team is looking to juice turnout is northeastern Pennsylvania, a predominantly white and working-class area that went from supporting President Barack Obama twice to Trump in 2016. The region is currently the campaign’s focus for its ground-game operation in the state, according to a Trump aide. The president is also holding a rally in the region’s Luzerne County on Monday.

“It’s important for either campaign, but especially the Trump campaign because they've made such incredible inroads in the northeast and the Wyoming Valley in particular,” said Charlie Gerow, a Pennsylvania-based GOP consultant. “There are a lot of votes there and a lot of votes to be picked up by Donald Trump, including first-time voters. A ground game really does make a difference when you're going to the first-time voters.”

Democrats know that Trump has a solid base of support in northeastern Pennsylvania, but they are convinced that Biden will finish more strongly in the area than Hillary Clinton did in 2016, in part because of his hometown appeal in Lackawanna County, where Scranton is located. The Biden campaign specifically said it is doing better with white women and seniors in the northeast, and that there are not many more potential Trump supporters for him to mine after his blowout there four years ago.

“Luzerne County is hard, obviously. It's become very difficult for Democrats to win. But I think he'll cut the margins from 2016 there substantially,” said Democratic Sen. Bob Casey, who is close to the Biden campaign. “I think he’ll carry Lackawanna, and I think he’ll carry it decisively. With Donald Trump, I think it’s hard to get the margins that Democrats used to get there. But I think it’ll be above ’16 and below ’12.”

Democrats are also very confident in Biden’s ability to draw even more voters out of Philadelphia’s suburbs than Clinton did. The region helped flip several state legislative and U.S. House seats in 2018, as well as GOP-controlled county governments a year later.

Trump’s rallies on Saturday were symbolic of his challenges — and the political divides — in the state. While Butler County’s event drew thousands of his fans, his stop in suburban Philly’s Bucks County on Saturday, which appeared to be invite-only, was much smaller than his typical events.

A Franklin & Marshall survey released last week also served as a red flag for Trump’s strategy to find more support in places he won in 2016: It showed Biden not only outperforming Clinton in counties she carried, but also Trump getting a slightly smaller share of the vote in counties he took.

Trump’s campaign believes that its ground-game operation will swamp Biden’s, however. In an effort to limit the spread of Covid-19, Biden’s team did not knock on voters’ doors until October, which Trump’s aides believe will make it difficult for him to turn all of his supporters into voters.

“I don’t understand why they’re not doing any canvassing or get-out-the-vote. In 2016, the Clinton people boasted about their ground game,” said Rob Gleason, the former chairman of Pennsylvania’s Republican Party. “We started working our ground game a year ahead of time. You can’t just turn this on and off.”

Trump’s allies also think that he will limit his losses in Philadelphia this year, particularly among young Black men. While in the city’s suburbs Saturday, Trump tried to dampen support for Biden among the voting bloc, telling rally-goers, “For 47 years, Joe Biden betrayed African Americans at every turn. He took your votes, he took you for granted, and then he shipped away your jobs and flooded your cities with cheap foreign labor. He devastated Black families with his 1994 crime bill.”

Some Black leaders and activists in the city have raised alarms about what they said is a lack of excitement for Biden among young African American men.

“Every day that I was on the street, at least that first week, a young Black male that looked to be under 40 or under 45 told me in secret that they were voting for Trump,” said Nicolas O'Rourke, organizing director for the Working Families Party in Pennsylvania, which is running a get-out-the-vote operation backing Biden. “I have seen and heard folks that they just could not get behind any of them. Many Black men are honestly disgusted by the Republican Party, but also very much so done and over the Democratic Party and have chosen just to sit out.”

Despite anxiety among some local Democrats, Biden’s team has expressed confidence in its ability to turn out voters of color in the city. In a visit last month, Biden dispatched Obama to Philadelphia in part to speak directly to Black men. Biden also stumped at a “Souls to the Polls” event Sunday in the city.

Brendan McPhillips, Biden’s Pennsylvania state director, pointed to the fact that upward of 90 percent of eligible Philadelphians are registered to vote: "We haven’t seen numbers like that in decades."

But many Democrats are also deeply concerned about what they said is Trump’s attempt to steal the election in Pennsylvania. Democrats expect Trump’s campaign may challenge mail-in ballots that arrive up to three days after Nov. 3., which the state Supreme Court said must be counted if they are postmarked by Election Day or there isn’t a “preponderance of evidence” they were sent afterward, a ruling that the nation’s highest court left in place for now.

A Republican official told reporters Friday that “if it’s really close, to be frank, these ballots are going to become a point of contention.” Biden’s campaign does not think the late-arriving ballots will tilt the election — or that such a challenge would be successful.

Shapiro, the state attorney general, echoed that sentiment.

“Past is prologue. Every single legal fight Donald Trump has started with us, he’s lost and we’ve won,” he said. “And if he wants to pick another fight and try and stop ballots from being counted, then that one, too.”

Anita Kumar contributed to this report.