Owen Diaz had seen swastikas in the bathrooms at Tesla’s electric-car plant, and he had tried to ignore racist taunts around the factory.
“You hear, ‘Hey, boy, come here,’ ‘N-i-g-g-e-r,’ you know, all this,” said Mr. Diaz, who is African-American. Then, a few hours into his shift running the elevators, he noticed a drawing on a bale of cardboard. It had an oversize mouth, big eyes and a bone stuck in the patch of hair scribbled over a long face, with “Booo” written underneath.
On that winter night in the factory, when, he said, a supervisor admitted drawing the figure as a

