Voters’ views on impeachment seemed to hew to their deeply dug-in feelings about Mr. Trump. But often, as in Ms. Broadhead’s case, those views were detached from voters’ longstanding party allegiances.

It reflected Mr. Trump’s dueling influences in this critical swing district: His alienation of suburban Republicans and independents, and his appeal to white blue-collar voters who once supported Democrats. Bucks County, while trending Democratic, has plenty of both, a microcosm of how Mr. Trump has scrambled partisan allegiances nationwide based on education level.

Come November 2020, impeachment may well have faded from voters’ minds, given the scandal exhaustion of the Trump era. But some voters said the Trump presidency would remain tainted, coloring the election.

Another Bucks County voter untethered from his original party, Mike Corrigan, said he was once a Democrat but is no longer. “I think the Democrats didn’t like Trump from day one and they’re just looking for anything and everything they can’’ to use against him, said Mr. Corrigan, who is retired from the TV cable industry. “That turns me sour real bad.’’

In local Pennsylvania elections last month, Democrats made historic gains in the Philadelphia suburbs. In Delaware County — where legend has it that only registered Republicans could get their trash picked up — Democrats won a majority on the County Council for the first time since the Civil War. In nearby Chester County, Democrats wrested control of the courthouse for the first time.