"I think we’re kind of safer on the Democratic side going with a white male right now"

But as Mr. Biden prepares for his first appearance of the campaign, at a union event in Pittsburgh on Monday, interviews across the state last week indicated that he draws from a wellspring of support among three key constituencies crucial to his campaign. He has the potential to attract suburban moderates defecting from the Republican Party under President Trump, to invigorate black voters who were underwhelmed by Hillary Clinton and to reverse at least some losses among working-class white voters.

At Uncle Bobbie’s Coffee & Books in the Germantown neighborhood of North Philadelphia, black empowerment was on prominent display via titles like “White Fragility” and “What Doesn’t Kill You Makes You Blacker.”

But when the talk turned to presidential politics, patrons universally said Mr. Biden was at or near the top of their list, in no small part because of his eight-year partnership with President Barack Obama.

“Just to be in the house and assisting Barack when he was in the house, he would already have my vote for that alone,” said Ciarra Walker, 30, a small-business owner.