Mr. Trump, unlike previous incumbents, has done little to reach beyond his core supporters. Since the killing of George Floyd by the police in Minneapolis, the president has played to white voters with racist and inflammatory messages about protesters, Civil War monuments and crime.
Bernadette Comfort, the chair of Mr. Trump’s campaign in Pennsylvania, disputed that he was running a base-only strategy.
“The president in fact appeals to the single mom in suburbia, the president appeals to the working-class Republican, Democrat, whatever,” Ms. Comfort said. “We will go after independents, Democrats, after those folks who did not come out in 2016.”
Nonetheless, the Times poll showed erosion in the president’s base. Mr. Trump was favored by 86 percent of Pennsylvanians who said they voted for him in 2016, down from 92 percent in a Times poll in October.
In contrast to western Pennsylvania, the growing and racially diversifying counties outside Philadelphia have moved in the opposite direction. Four years ago, registered Republicans outnumbered Democrats by more than 18,000 in Chester County; today, Democrats have an edge of about 1,000.
Shivani Jain, a bank analyst in Chester County, is among the 47 percent of Pennsylvanians with a “very unfavorable” view of Mr. Trump, leaving him a very narrow path to win the state. Ms. Jain, 25, has participated in recent protests.
“As a person of color myself, I find the last few years has been heartbreaking,” she said. “I’m hoping with what I’m seeing with the Black Lives Matter movement and how many of my generation have come out, people take that energy to the voting booth.”