A Democrat won a surprise victory on Tuesday in a special election for the Pennsylvania State Senate, narrowly prevailing in a district that Donald Trump won by 15 points last fall.

The election, conducted in the small towns and suburbs of Lancaster County where no Democrat had won since the district was redrawn decades ago, joined two currents that are powering the political moment. It underscored the galvanizing fury among Democratic voters, who have flocked to rallies and crowded town hall meetings in the early weeks of Mr. Trump’s second term. And it was further evidence of the changes in the two parties’ electorates, with Democrats drawing more and more of the kind of highly educated voters who reliably turn out for special elections.

The victory does not affect control of the state senate, where Republicans now hold a four-seat majority, though another special election, near Pittsburgh on Tuesday, gave the Democrats a one-seat majority in the Pennsylvania House of Representatives. The outcome of the House special election was not a surprise, but the margin of the Democratic victory there also exceeded Kamala Harris’ performance in the district in 2024.

The winner of the state senate election, James Andrew Malone, 51, is a heavy-bearded, soft-spoken I.T. consultant who has been mayor of East Petersburg Borough, a small town northwest of the city of Lancaster, for the past seven years.

He defeated Josh Parsons, the chairman of the Lancaster County commission and an outspoken pro-Trump conservative. Mr. Parsons was strongly favored in the district, where Republicans hold a substantial registration advantage.

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