Twelve killed at Columbine High in 1999. Thirty-two people murdered at Virginia Tech in 2007. Six killed and 13 wounded, including then-Congresswoman Gabrielle Giffords, in Tucson, Ariz., last year. Twelve murdered by a gunman in Aurora, Colo., in July.

If there was a tipping point on serious policy to prevent mass killings, the nation should have reached it long ago. But Friday's massacre in Connecticut – claiming the lives of 20 elementary school children and seven adults – has clearly changed the dynamic. More and more elected officials agree that now is the time to confront the root causes of these national tragedies – easy access to guns, a threadbare mental health system and video games and movies that glorify gun violence.

In his comments Friday and then Sunday, President Barack Obama has made clear he's prepared to invest real political capital on gun control. While the president has his hands full with the "fiscal cliff," he should seize the moment. Even ardent gun-rights supporters – such as Joe Manchin, a Democrat from West Virginia – have signaled they are prepared to talk about restrictions on certain guns because of the horrors committed at Sandy Hook Elementary School.

The first need is for Congress to enact a new ban on semiautomatic weapons, known as assault rifles, such as the Bushmaster .223 model used by Adam Lanza to kill so many of his victims. The law needs to be stronger than the previous federal assault weapons ban, which expired in 2004 and has lapsed because of lobbying by the National Rifle Association and other groups.

Congress should go further, however. It should set up a buyback program to reduce the existing legal stockpile of assault weapons, as Australia and other nations have done. It should require a mandatory background check for all gun purchases, including private sales. It should put limits on the size of rifle magazines, such as 100-round drums that make it easy for assailants to spray bullets into a crowd. It should follow California's lead and require a microstamp on each shell so police can more easily trace it back to a particular gun.

Although California has been ahead of Congress and most states, it could be tougher on gun control. Last year, the Assembly shelved legislation by Sen. Leland Yee, D-San Francisco, that would have closed a loophole in the state's assault weapon ban and prevented such weapons from having devices known as "bullet buttons," which allow them to be easily reloaded with multiple rounds of ammunition.

In addition, Gov. Jerry Brown vetoed legislation, Senate Bill 1366, which would have required gun owners to report the theft or loss of any gun within 48 hours.

State and federal lawmakers will have to stand up the the gun lobby to get such common-sense measures passed, but the tide is turning against these hard-line groups and their spurious arguments.

Following Friday's mass murder, the leader of Gun Owners of America, Larry Pratt, suggested that it could have been prevented if teachers had been allowed to carry firearms to the elementary school. "Gun control supporters have the blood of little children on their hands," Pratt is quoted as saying.

Pratt's rantings conveniently ignore the fact that Nancy Lanza owned multiple weapons that did nothing to save her life. Indeed, one of those weapons was used against her by her deranged son, according to police.

Skeptics are correct that no combination of laws can fully prevent a madman from carrying out his carnage. But stronger gun laws – combined with less violent media culture and better detection of potential psychopaths – could undoubtedly save lives. Even if such measures prevented a single Sandy Hook in the future, it would be worth it.

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