More than two decades before Newtown, there was Stockton.

In January 1989, a troubled drifter in his 20s opened fire with a semiautomatic rifle on a California elementary school yard packed with students. Five children, ages 6 to 9, were killed in the fusillade of bullets; 29 others were wounded, along with one teacher.

The resulting national shock and outrage plunged Congress into a debate over whether to ban military-style assault weapons.

“The American people are fed up with the death and violence brought on by these assault weapons,” Senator Howard M. Metzenbaum, an Ohio Democrat, declared on the Senate floor. “They demand action.”...