“In the past, we hadn’t really been like, ‘O.K., here’s where we stand,’” said Lacy Simons, the owner of Hello Hello Books in the seaside town of Rockland, Me. Ms. Simons said she was jolted into action the day after the election, when customers began drifting into the store, not to buy books, exactly, but in search of solace.

“This is just one of the places where people went,” she said. “If they were gutted from the election, people just came in to pet the books.”

Her plans to push back against Mr. Trump’s policies are just beginning: Later this month, the store’s new social justice reading and action group will meet for the first time (suggested reading: “What We Do Now: Standing Up for Your Values in Trump’s America”). She also intends to distribute political leaflets and other materials to customers, on the model of bookstores that handed out mimeographed resistance newspapers during the Vietnam War.

Stephanie Valdez, an owner of Community Bookstore in Brooklyn, has already hosted a postcard-writing event, and lately she has paged through books on political organizing, looking for guidance for getting her store more involved.

“I think bookstores are a place where people go to understand the world,” she said. “And I think we’re just one of many places that will become a center of activism.”

Gayle Shanks, a co-owner of Changing Hands in Phoenix, said her store’s Facebook page had gone political, as staff members filled it with articles about national politics and First Amendment issues. At the suggestion of one of her young employees, staff members began piecing together a display of books written by authors from the seven majority-Muslim countries from which Mr. Trump suspended immigration.