Joseph A. Califano Jr. was President Lyndon B. Johnson’s top assistant for domestic policy. He was secretary of health, education, and welfare in the Carter administration and is Founder and Chair Emeritus of the National Center on Addiction and Substance Abuse at Columbia University.

Ifever there were a moment for President Obama to learn from history, it is now, in the wake of Friday’s shootings at the elementary school at Newtown, Conn. The timely lesson for Obama, drawn from the experience of Lyndon B. Johnson — the last president to aggressively fight for comprehensive gun control — is this: Demand action on comprehensive gun control immediately from this Congress or lose the opportunity during your presidency.

In the aftermath of the assassination of Robert F. Kennedy (just weeks after the fatal shooting of Martin Luther King Jr. and only a few years after President John F. Kennedy was shot), President Johnson pressed Congress to enact gun control legislation he had sent to Capitol Hill years earlier. LBJ ordered all of us on his staff — and urged allies in Congress — to act swiftly. “We have only two weeks, maybe only 10 days,” he said, “before the gun lobby gets organized.” He told Larry O’Brien and me, “We’ve got to beat the NRA [National Rifle Association] into the offices of members of Congress.”...