WASHINGTON — Pennsylvania is rapidly turning into a crucial battleground state in the presidential election.

This week in Pennsylvania:

■ U.S. Sen. JD Vance of Ohio, the Republican vice presidential nominee, was in New Kensington on Thursday.

■ Former President Donald Trump, the GOP presidential nominee, will speak Saturday in Wilkes-Barre.

■ Vice President Kamala Harris and Minnesota Gov. Tim Walz, the Democratic presidential and vice presidential nominees, will be in Pittsburgh on Sunday with their spouses to kick off a bus tour of Western Pennsylvania before the party’s national convention begins Monday.

“There’s little doubt that the path to the presidency runs through Pennsylvania,” said Berwood Yost, director of the Center for Opinion Research at Franklin & Marshall College. “Both campaigns see it that way. That’s why they're here.”

Besides amassing frequent flyer miles, both sides have been blanketing Pennsylvania airwaves with campaign ads.

The GOP already has spent more on the 2024 election than it did in 2020, $140 million versus $105 million, according to the ad tracking firm AdImpact. Trump defeated several other Republican candidates to win the nomination this year.

Democrats have spent less — $230 million for the 2020 election and $140 million so far in 2024, but their contested primary was four years ago.

The figures include reserved airtime.

In fact, when combined with the almost $215 million on commercials for the state’s U.S. Senate race, nearly half a billion has been spent in Pennsylvania thus far.

The Harris campaign announced Wednesday it would spend another $90 million in Pennsylvania and other battleground states this month.

“It is precisely through efforts like this that we will break through a crowded media environment early and make clear the choice and stakes of this election for the voters who will decide it,” said Quentin Fulks, principal deputy campaign manager for the Harris campaign.

The visits and this new spending come after the substitution of Harris for Biden atop the Democratic ticket dramatically shook up the race in Pennsylvania and elsewhere.

The Pew Research Center reported Wednesday that Democratic enthusiasm for Harris had equaled that of Republicans for Trump. In the Pew survey, 62% of Harris supporters and 64% of Trump supporters back their candidates strongly. Just 43% of Biden supporters backed him strongly in a poll released last month, while 63% of Trump supporters strongly supported the former president. The survey of 9,201 adults was conducted Aug. 5-11 and had a margin of error of plus or minus 1.3 percentage points.

While the results of three recent Pennsylvania polls all were within the margin of error, all three also showed Harris ahead of Trump.

A Franklin & Marshall College poll released Thursday gave Harris a 46% to 43% edge when third-party candidates are included. That survey of 902 voters was conducted July 31-Aug. 11 and had a margin of error of plus or minus 3.8 percentage points.

Harris led Trump in Pittsburgh and the rest of southwestern Pennsylvania, and in Philadelphia and its suburbs. Trump led in the rest of the state.

The Harris campaign recently announced it would send Walz to four rural counties in the central part of the state with an eye toward holding down Trump’s margins there.

Separately, a Quinnipiac University poll released Wednesday put Harris ahead, 48% to 45%, with third-party candidates, and by 50% to 47% in a two-way race. The survey of 1,738 likely voters was conducted Aug. 8 to 12 with a margin of error of plus or minus 2.4 percentage points.

And a Cook Political Report survey, also released Wednesday, gave the vice president a 48% to 43% edge over the former president with third-party candidates added and 49% to 48% head to head. That poll of 411 likely voters was taken July 28-Aug. 2 with a margin of error of plus or minus 4.8 percentage points.

“The evidence was in front of us for a long time that there were a lot of people who did not like the choices they were offered,” Yost said. “Changing those choices has changed the race.”

For example, Harris has the support of 100% of voters who described themselves as progressive Democrats and 96% who said they were centrist Democrats in the F&M poll. Biden, however, was backed by only 89% of progressives and 93% of centrists in F&M’s April survey.

“Kamala Harris has injected some energy into the Democratic base,” Yost said. “She really brought those folks home.”

Trump’s share of support from traditional Republicans, such as those who presumably backed former South Carolina Gov. Nikki Haley, rose from 73% in April to 84% in August. Haley had received more than 155,000 votes, or 17% of the total, in the April Pennsylvania primary even though she was no longer a candidate. She endorsed Trump and spoke on his behalf last month at the Republican National Convention.

In the F&M poll, independents in April gave 48% of their support to third-party candidates Robert F. Kennedy Jr. or Jill Stein. Now, they're down to 21%. And while 4% of Democrats backed either candidate in April, none of them do now.

“It’s pretty clear that both bases are where they should be,” Yost said. “The fight comes down to independents, as you might expect.”

Also in the F&M poll. U.S. Sen. Bob Casey, D-Pa., had a double-digit lead over his Republican challenger, former hedge fund CEO David McCormick, 48% to 36%. That's the same 12-point margin as in February.

That's despite Casey’s job approval rating being in negative territory, with 46% disapproving and 38% approving.

Gov. Josh Shapiro’s job rating was positive, with 51% approving of his performance in office and 40% disapproving.

The poll did not ask about U.S. Sen. John Fetterman, who is not on the ballot this fall.