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."

For three years Johnson’s bill had been locked in the Senate Judiciary Committee by a powerful army of gun lobbyists. But LBJ was always poised to grasp any opportunity to achieve his legislative objectives, even in the most horrendous circumstances. He had used the tragedy of King’s assassination in 1968 to "at least get something for our nation" out of it, finally persuading the House to pass the Fair Housing bill he had sent it in 1966. Johnson saw in the tragedy of the assassination of Robert Kennedy in June of 1968 a chance to get his gun bill enacted...