PITTSBURGH — Saturday morning in the city’s Strip District business neighborhood, about 100 people were gathered on the corner of Smallman and 21st streets, drinking coffee, cocoa, and hot cider. They came from all ethnic and socioeconomic backgrounds and were all essentially strangers except for one common purpose: They were standing there on that brisk fall morning holding up signs in support of Donald J. Trump.

The mood was happy. Despite being masked up, they enjoyed banter with strangers who came up to chat or gave broad smiles to people who waved or beeped their horns as they passed by, including the ones who gave them a single-finger salute.