Marty Trombetta says the affluent suburbs north of Pittsburgh haven’t changed much since she moved to the area 35 years ago. Large houses with manicured lawns still dot the winding, tree-lined streets that many conservatives call home.

But as the 2020 election approached, it became clear that attitudes toward politics had shifted. Trombetta, 62, said friends who had supported Republican candidates their whole lives, even some who voted for Donald Trump in 2016, told her they’d reached a breaking point.

“Trump’s lack of integrity, his vitriolic rants, his missing moral fiber. It all became too much for people,” said Trombetta, a homemaker who grew up outside Philadelphia in West Chester and now lives in Richland Township, about a half-hour north of Pittsburgh. “They voted for Joe Biden for the good of the country.”

Biden has suburban voters like these partly to thank for his narrow victory in Pennsylvania, and for making him president-elect. Biden ran up huge margins in Philadelphia’s suburbs. But he also delivered a commanding performance in Pittsburgh’s suburbs, winning Allegheny County by 38,000 more votes than Hillary Clinton did in 2016 — almost half his final statewide margin of victory of about 81,000 votes.

An epicenter of that shift was Pine Township, the North Hills town next door to the one where Trombetta lives. While Trump narrowly won Pine, Biden improved on Clinton’s 2016 performance there by more than 7 percentage points, one of the biggest swings in the county. In four of the five Allegheny County towns that surround Pine — McCandless, Franklin Park, Marshall, and Bradford Woods — he did at least 5 points better than Clinton.

» READ MORE: How Joe Biden won Pennsylvania

At the root of Biden’s success in this part of the state are the scores of wealthy, college-educated voters in historically Republican areas who rebuked the president. But political strategists in both parties caution that, unlike in wide swaths of the more liberal Philadelphia suburbs, Democrats may find it harder to win Allegheny County voters when the election isn’t a referendum on Trump.

The first major test of whether Biden’s coalition in the Pittsburgh region is truly a Democratic one or merely one that mobilized to oust Trump will come in 2022, when Pennsylvania voters are set to pick their next governor and U.S. senator. Both are open-seat races, with Democratic Gov. Tom Wolf term-limited and Republican Sen. Pat Toomey not seeking reelection.

And in a warning sign for Democrats, Biden’s strength didn’t extend to elections down the ballot, where they suffered bruising losses in legislative races — including the defeat of State Rep. Frank Dermody, the House Democratic leader who represented part of Allegheny County.

“Is it easier for a Republican to claw back suburban votes or for Democrats to claw back blue-collar votes?” asked Mark Harris, a Republican strategist based outside Pittsburgh. “I think Republicans have to really roll up their sleeves and fight. We’re now the party of the working class, which is great. But to get to a majority, the battle lines are going to continue to run through the suburbs.”

Ben Forstate, a Democratic political analyst who has worked on campaigns in the area, said the question is not whether the North Hills will continue to shift Democratic, but how fast. The region is older and whiter than the Philadelphia suburbs, making it more competitive politically.

“Pine, Richland, and these other towns are all trending Democratic, and there’s more political activism there than there’s ever been,” Forstate said. “That change won’t stop, but it might slow down.”

In 110 of Allegheny County’s 130 municipalities, voters supported Biden at higher rates than they supported Clinton.

Biden’s biggest gains in total votes came in Pittsburgh, where Democratic turnout increased by 8% compared with 2016 while Trump’s support stayed relatively flat. As a result, Biden had a 92,000-vote advantage over Trump in the state’s second-biggest city, up 7,800 over Clinton’s margin. In Philadelphia, by contrast, Trump actually cut into the Democrats’ advantage this year.

But within the Allegheny communities that shifted toward Biden, enthusiasm for his candidacy was hardly universal.

Trombetta said many of her friends and neighbors are Republicans. Even her parents, who raised her as a Democrat, support Trump now.

“They saw him for what he claimed to be, not what he turned out to be,” Trombetta said. “And I think a lot of them were thinking about their pocketbooks, as sad as that is.”

She survived the ugly presidential campaign by leaning on like-minded women. A group text-message thread that started with four people eventually grew to 10. They used the forum to share research debunking the president’s false statements or sometimes just to vent or encourage one another. They called themselves SWAT — Suburban Women Against Trump.

They didn’t talk much about down-ballot races. Maura McAnney, 58, another member of the group, said she wasn’t surprised support for Biden in the historically conservative suburbs didn’t translate into victories for other Democrats.

“People who have traditionally voted Republican didn’t want to abandon the GOP entirely,” said McAnney. “They wanted to rebuke Trump.”

» READ MORE: The Philadelphia suburbs were the key to Joe Biden’s Pennsylvania victory. Here are the numbers.

Democrat Emily Skopov, a nonprofit executive, had hoped to ride a blue wave and replace retiring Republican Mike Turzai in the state House. He was speaker of the House and the latest in a long line of Republicans who had held the seat for decades.

But even though Biden narrowly won the district, Skopov lost by 7 percentage points to Republican Rob Mercuri, a bank executive who served as a military intelligence officer in Iraq. The race in Pennsylvania’s 28th District was one of several competitive contests Republicans won, dashing Democratic hopes for a takeover of the state House.

“Voters in these transitioning areas, they aren’t fully on board with the Democratic Party,” said Mike Mikus, a Democratic strategist from the area.

Mikus recalled that when he ran Democrat Rich Fitzgerald’s first campaign for Allegheny County executive in 2011, Fitzgerald lost Upper St. Clair by a 2-1 ratio. Located 10 miles southwest of Pittsburgh, the town has residents who are mostly white, affluent, and college-educated. This year, Biden won 54% of the vote there.

“It just shows the dramatic change in these suburban communities,” Mikus said.