The 1960s were known for their turmoil, but the degree to which guns were a factor is sometimes overlooked. Not only was a president assassinated, but an ex-Marine opened fire from an observation deck in Austin and the homicide rate leaped by more than 50 percent, driven by fatal shootings. Gun sales soared, prompted by fears of violence and rioting.

But the mayhem and violence didn’t seem to move a Congress that refused to take gun-control legislation seriously. It would not even approve a proposal to outlaw the mail-order purchase of rifles, like the one Lee Harvey Oswald bought for $19.95, plus shipping and handling, and used to kill President Kennedy.

One of the few major gun control measures enacted, in California, was a reaction not to violence but to the Black Panthers’ exercising their right to bear arms by patrolling with loaded rifles.

The political calculus began to change on April 4, 1968. The Rev. Dr. Martin Luther King Jr. was gunned down in Memphis. Nine weeks later, Senator Robert F. Kennedy was fatally shot in Los Angeles.