...Mr. Beymer admitted that he was not thinking in such lofty terms back in 1964. He ended up in Mississippi because his agent told the opinionated young actor to do something about the terrible conditions in the country or shut up about it, he said. That summer of activism and friendship, including his first bonds with African-Americans, was both transformative and jarring, Mr. Beymer recalled.

Once, on his way to Biloxi, a police officer pulled him over. His crime: having a young black man beside him in the two-seater. “He was just railing at me,” Mr. Beymer said of the officer. “In the meantime, a pickup truck pulled in the back of the squad car. Rebel flag. Gun rack.” The officer told him, using an expletive: “Those boys up there are not going to be as lenient as me. Now this is what you’re going to do. Get that ”person“ back in the car, and you get out of here. And if I see you again, I will kill you.”...