Most Democrats still believe Biden will capture Pennsylvania, and he maintains a modest polling lead there, but their confidence has eroded in recent weeks with emerging signs of a tightening contest in the state, according to elected officials, strategists and party activists. Both sides believe the outcome in Pennsylvania will be crucial in determining who wins the White House.

The causes of Democrats’ anxiety are varied. They worry about potential trouble with mail-in ballots during a pandemic. They are concerned about the prospect of a voter surge in White, rural areas favorable to Trump and signs of lower-than-anticipated turnout among the Democratic base.

They are nervous about GOP efforts to place limits on voting. They cringe at the recent looting and violence in Philadelphia, which Trump has seized on to portray Biden as weak on crime and hostile to police. And they harbor lingering concerns about Biden’s muddled rhetoric on oil and gas, which has prompted inaccurate attacks that he advocates ending fracking…

Many Democrats acknowledge that their doubts may be exaggerated by what happened four years ago, when Trump shocked analysts by narrowly winning Pennsylvania — a loss that Democrats did not see coming and have yet to fully recover from emotionally. Since then, consistent Democratic electoral gains in Pennsylvania have prompted Republicans’ own alarms about the state.