In this Tuesday, Nov. 5, 2019, photo Delaware County Council candidate Elaine Schaefer, third from right, wearing glasses, takes a selfie with supporters after the Delaware County Democratic Committee's election watch party at the Inn at Swarthmore in Swarthmore Pa. (Tim Tai/The Philadelphia Inquirer via AP)

In this Tuesday, Nov. 5, 2019, photo Delaware County Council candidate Elaine Schaefer, third from right, wearing glasses, takes a selfie with supporters after the Delaware County Democratic Committee's election watch party at the Inn at Swarthmore in Swarthmore Pa. (Tim Tai/The Philadelphia Inquirer via AP)

HARRISBURG, Pa. (AP) — Democrats completed an electoral sweep of Philadelphia’s four suburban counties in Pennsylvania, long a bastion of Republican control and a critical bellwether for statewide candidates.

Democrats won control in Delaware and Chester counties in Tuesday’s election for the first time going back to the Civil War and won control in Bucks County for the first time since the 1980s.

Democrats took control of Montgomery County eight years ago. The fast-growing counties now account for more than one in five of all registered voters in Pennsylvania, and they tend to vote in higher proportions than the rest of the state.

The Democratic victories in Delaware and Chester counties were particularly strong, winning every countywide race, including contests for county council, district attorney and county judge.

For three decades, the counties had been growing increasingly liberal, but the trend seems to have accelerated since Donald Trump’s election as president.

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Alan Novak, a former state Republican Party chairman from Chester County, said strong Democratic results in Philadelphia’s suburbs Tuesday reflect voters motivated against Trump and by good candidates, good campaigning on local issues and the lure of capturing control of county government.

“They gave their voters a reason to come out and that was, ‘For the first time in history, we can be a majority in the courthouse,’ and that’s a big motivator,” Novak said. “There’s the Trump factor, there was the local factor.”

Chester County’s Democratic Party still trails the Republican Party in overall registration.

But Democrats are appealing to Republicans there on issues such as environmental protection, health care and gun control, while Democrats have a heavy registration edge with voters there who are 40 or younger, said Chester County’s Democratic Party chairman, Dick Bingham.

Trump lost badly in Philadelphia’s suburbs in 2016, although Republicans in those four counties still held onto many down-ballot offices that year. Since then, the GOP has lost dozens of offices there, including two congressional seats and a majority of state legislative seats for the first time in modern history.

Republicans were not without victories, albeit in areas of Pennsylvania where the population is stagnant.

In western Pennsylvania, where Democrats have been losing seats for the past two decades, Republicans took back control in Armstrong, Greene, Washington and Westmoreland counties.

In other areas, Democrats appeared to have won control in Lehigh County, giving the party a majority on the county board of commissioners for the first time in four decades.