One reason for his growing lead, the surveys suggested, is that Mr. Biden is more well liked than Mrs. Clinton was by voters. Fifty percent of Pennsylvania voters have a favorable view of Mr. Biden, according to a New York Times/Siena College Poll in June. That is notably stronger than the 42 percent of voters with a favorable view of Mrs. Clinton in exit polls of the state four years ago.
It partly explains why Mr. Trump, who is doing little to grow support beyond his fervid base, is trying to drive up enmity for Mr. Biden through scorched-earth attacks, in order to depress turnout for him.
Old Forge, a town where Italian immigrants arrived a century ago to work in coal mines, long since closed, is best known today for a style of rectangular pizza. Mr. Trump’s promise in 2016 to stop undocumented immigration, restore factory jobs and to take on China resonated deeply with the area’s white voters, as it did across other industrial states.
Calling Mr. Biden “no friend of Pennsylvania” on Thursday, the president charged that Mr. Biden’s support for trade deals as a senator had taken a disastrous toll, while he distorted Mr. Biden’s climate plan to claim it would end drilling for oil and gas.
Mr. Biden visited a metalworks factory near Scranton last month to lay out a New Deal-style plan for economic recovery from the virus, promising to create five million manufacturing and innovation jobs across the country. His advisers consider Mr. Trump’s advantage with voters on jobs and the economy to be Mr. Biden’s greatest vulnerability.
Republicans have begun to narrow a historic gap with Democrats in registered voters in Lackawanna County. Since November of last year, Republicans added 2,469 registered voters, versus 459 new registered Democrats. The Democratic brand is so tarnished locally that Mayor Paige Cognetti of Scranton, a former official in the Obama administration, ran last November as an independent.
“It does surprise me that so many people have registered that way,” said Ms. Cognetti, who endorsed Mr. Biden. Referring to the pandemic and record unemployment of 15.3 percent in Lackawanna County, she added, “To me the Democrats are the party that is going to get us through this crisis.”