Susan Page

USA TODAY

The USA TODAY Network is spending time in eight counties in eight states, exploring the key electoral themes that could decide this fall’s election. Each week from now until the election, we will feature a different one. The series debuted last week with a look at Waukesha County in Wisconsin. Today: Chester County in Pennsylvania.

WEST CHESTER, Pa. — At age 48, Patty Mapa can't remember ever voting for a Democrat for president.

Then Republicans nominated Donald Trump.

The substitute kindergarten teacher, who was shopping for fresh produce with her husband and daughter at the West Chester Growers Market in this Philadelphia suburb on a recent day, worries the billionaire businessman is "negative, just very divisive, and erratic." She's less than thrilled about casting her ballot for Democrat Hillary Clinton — "There's that dark little cloud" when it comes to trustworthiness, she says — but on this Mapa is certain: "I am voting against Trump."

The biggest swing in the American electorate this year is happening among white, college-educated voters like Mapa. They are a big and growing group — an estimated 23% of the electorate four years ago and expected to be a bit more this year — and they have voted Republican in every presidential election since at least 1952. Four years ago, Mitt Romney won their support by a solid 14 percentage points, according to surveys of voters as they left polling places. But in the latest Pew Research Center poll, taken last month, Clinton led among whites who have a college degree by 14 points.

That may be the most dramatic partisan shift by a major demographic group from one presidential election to the next in modern American history.

The Deciders: A look at 8 key counties that are going to help decide this election

In places like Chester County in Pennsylvania, Douglas County in Colorado, Delaware County in Ohio, Wake County in North Carolina and Fairfax County in Virginia, those changing allegiances create formidable problems for Trump in states he needs to win the White House. While national polls give the businessman and reality TV star a 2-1 lead among white voters who don't have a college education, Democrats' traditional appeal among minority voters and their new strength among better-educated whites, especially women, risk making an electoral majority all but out of reach for him.

Pennsylvania is a crucial state. Trump, Clinton and running mates Mike Pence and Tim Kaine all have campaigned here since the Democratic convention, and the Clinton campaign also has sent in Vice President Biden and former president Bill Clinton.

On a sunny Saturday near summer's end, the weekly farmers market tucked on an open lot in downtown West Chester is bustling with shoppers eyeing stacks of tomatoes and corn, six kinds of apples, early pumpkins and gourds, and homemade pies and cobblers.

Margot McKee, who works in real estate sales (and describes her age only as "old enough to know better") bought a maple oat muffin to eat later. In April, she voted for Trump in Pennsylvania's GOP primary. He trounced his rivals, winning 57% of the vote over Texas Sen. Ted Cruz (22%) and Ohio Gov. John Kasich (19%). But now she anguishes over what to do in November.

"I think he's done a great job in getting people's attention to some issues that have been neglected, and Congress is dysfunctional and politicians are dysfunctional, and they don't seem willing to do their jobs," she begins. But she says Trump needs to "grow up and learn to keep his mouth shut," first describing him as "impossible" and then calling him an unprintable epithet.

What about Clinton? McKee sighs. "I'm drawn to her because of her experience and her even manner, but I'm not sure that she's honest," adding unhappily that "the Clintons seem to know how to duck and bob."

"I'm so disgusted I'm thinking that maybe I'm not going to vote," she muses, something she's never done before. "But then, that's a cop-out."

The four "collar counties" around Philadelphia — Bucks, Chester, Delaware and Montgomery — in the past have provided Republican margins to help neutralize the Democratic advantage in the city itself. In the past 12 presidential elections, Chester has voted for the Democratic candidate only once, in 2008. But Democrats have become increasingly competitive in the suburban counties, which include about a third of the state's voters. In 2012, Romney lost the other three and carried Chester by just two-tenths of a percentage point, the closest margin in the state.

Or, as West Chester Mayor Carolyn Comitta, a Democrat, ruefully recalls: "529 votes."

The county has a population of about 516,000, and half have college degrees — the highest proportion in the state. Average household incomes are well above the state average; unemployment is well below, and voter turnout is high. Four years ago, seven in 10 of the voting-age citizens in Chester cast ballots. The county's residents are overwhelmingly white. Just 6% are African American, 7% Latino.

Even so, it is Trump's provocative rhetoric about Mexicans, Muslims and immigrants that seems to have created the biggest backlash among Chester County voters.

"Typically here, it's having a fiscal conservative that's most important to Chester County voters, but this race is transcending traditional issues," Chester County Republican Chairman Val DiGiorgio, a lawyer, says. "What's important here and determinative here is whether Donald Trump can show himself to be someone who reaches out to a broader segment of the population, as opposed to what he did during the primaries. We're still waiting to see whether that's the case."

DiGiorgio, who endorsed Florida Sen. Marco Rubio in the Republican primary, now supports Trump and is "putting all our efforts to make sure he's elected president." He says the New York billionaire has drawn more volunteers than usual to the local GOP organization.

But the Republican county committee's home page — which among other things offers GOP-branded wine made from grapes grown in Chester County — on Monday didn't mention Trump's name or the presidential race. The website's tab listing "2016 candidates" included statewide and local contenders, but not the top of the ticket.

To be fair, the home page of the Chester County Democratic Committee didn't mention Clinton, either, though she was listed on the "2016 candidates" tab. But a banner across the top of the page declared: "If you don't vote the whole ballot, you are not doing your full part against Trumpism."

Just how much impact Trump could have down the ballot is a worry for Republicans and a hope for Democrats. In a statewide Franklin & Marshall College Poll taken last month, Clinton led Trump by 7 points, 47%-40%, and Democratic Senate challenger Katie McGinty led incumbent Republican Pat Toomey by 5 points, 43%-38%. The hard-fought Keystone State race is one of a handful expected to determine control of the Senate.

"The fact is she’s the beneficiary of Clinton emerging into the lead," G. Terry Madonna, director of the poll and a professor of public affairs, says of McGinty. "I think if it's five points or less, Toomey has a good chance of winning." But if Clinton wins the state by more than 5 points, Trump may leave Toomey with too much ground to make up among voters willing to split their ticket.

Comitta, who is challenging three-term Republican incumbent Dan Truitt for the state House of Representatives, enthusiastically backs Clinton. But she generally tries to talk about local and state issues, not the national race, as she campaigns. She stops by the farmers market after a morning of walking door-to-door on this recent day, distributing fliers that don't mention party affiliation, instead describing her as "Mom. Educator. Mayor."

"I hear from some people who love her, some people who would never vote for her, and some who will vote for her because they can't imagine Trump being president," she says of Clinton. "Because the two candidates are so polarizing, and I have to win my race, I'm not going there. ... That's a whole other conversation."

Truitt didn't return calls seeking comment.

Trump does have enthusiastic supporters in Chester County, and Linda Ives is one of them.

"You look at a human being as a body of work, and I think that the gentleman has without a doubt provided opportunities, job opportunities, for hundreds of thousands of people, and after watching his children at the convention, I was most impressed," says Ives, 54, a retired U.S. Army captain who now works as a consultant.

She also is motivated by fierce opposition to Clinton. She calls the former secretary of State "a criminal" for her role in the 2012 deaths of four Americans in Benghazi, Libya, and her carelessness with sending classified information on her private email server.

"If I had sent one unclassified email like that, I would be at Fort Leavenworth right now; I would be in jail," Ives says. She is concerned about Trump's "delivery," but she also says unfair news coverage is contributing to his problems.

"I think people are embarrassed to say they're supporting Trump," she says. "I think what's happening is — sorry, guys — the liberal media is just pushing the whole, 'The man is a ridiculous clown.' I mean, he's getting portrayed as a ridiculous clown, and the only people who are going to vote for him is the young, uneducated male. So people are then, 'I’m an educated person, why would I be stupid enough to vote for Trump?' "

Indeed, the electoral shift among college-educated whites in just four years has been of historic proportions, particularly for such a large group of voters.

"In Donald Trump, you have a perfect storm of a candidate in terms of pressing buttons to sending white, college-educated voters, particularly women, in the other direction," says Ruy Teixeira, co-director of "States of Change," a nonpartisan project that studies the impact of demographic trends on elections. "These are not voters who are protectionist or anti-immigrant. He represents a type of Republicanism or strand of the Republican Party that they probably like the least."

What's not clear yet is whether Republican-leaning voters like those in Chester County who plan to vote for Clinton this time will stick with Democrats down the road.

"Some of this is peculiar to Trump, but I do think that Trump's success reflects the way the bases of the two parties have changed," says political scientist Alan Abramowitz of Emory University. The 2016 race may accelerate long-term trends that are reshaping the historic perception of Democrats as the party of blue-collar workers and Republicans as the party of white-collar workers. "Especially at the presidential level, now Republicans are the party of the white working class," Abramowitz says.

Meanwhile, Lisa Cromley, 53, a middle-school English and history teacher, shops at the farmers market and then drops by a Democratic campaign storefront around the corner.

"I am so concerned about Trump that I don't know where to begin," she says, then ticks off a list. "I'm concerned that he doesn't know any issues; he's not a politician. He doesn't have a legal background; he really has a business background, and the business background he has isn't even something that I think translates. I'm concerned about his attitude toward most of the people who make up our pluralistic nation, our multicultural nation. I'm concerned that he doesn't think before he speaks."

She picks up a yard sign and a bumper sticker for Clinton, hoping the public displays of support will encourage voters who may be reluctant to support her.

"But I try not to talk to people about this campaign," Cromley adds. "It's so divisive."

To report this series, the USA TODAY Network identified eight counties around the country that represent key voting groups in the November election, from blue-collar and college-educated voters to rural voters and Latinos. Journalists spent time with voters, political observers and experts in these eight counties — blue, red and purple — talking about the presidential candidates, the issues and the importance of this year’s election.

Our first story looks at GOP “base” voters in Waukesha County, Wis. In our second story, we talk to white, college-educated voters in Chester County, Pa. In the coming weeks, look for our coverage of the following counties: Wayne County, Mich.; Maricopa County, Ariz.; Union County, Iowa; Larimer County, Colo.; Clark County, Ohio; and Hillsborough County, Fla.