— The question surfaces each time a mass murder unfolds: Will this one change the political calculus in Washington against tougher gun control?

The answer, after the Virginia Tech killings, the attempted assassination of Gabby Giffords, the Colorado movie-theater attack, the Wisconsin Sikh temple shootings, and more: No.

But now?

The massacre at Sandy Hook Elementary School in Newtown, Conn., the bloodiest attack against youngsters in the nation's history, stands as a possible tipping point after Washington's decade-long aversion even to talking about stricter gun laws.

So it seems in the stunned aftermath, judging from President Barack Obama's body language as much as his statement. "We have been through this too many times," said the famously composed president, this time moved to tears. "We're going to have to come together and take meaningful action to prevent more tragedies like this, regardless of the politics."

It remains to be seen whether Sandy Hook will break the usual cycle of universal shock fading into political reality. That reality is based on a combination of powerful gun lobbying and public opinion, which has shifted against tougher gun control and stayed that way. However lawmakers react this time, it's the president's call whether the issue fades again or takes its place alongside the legacy-shaping initiatives of his time, with all the peril that could mean for his party.

With the murder rate less than half what it was two decades ago, and violent crime down even more in that time, gun control has declined as a political issue.

But New York Mayor Michael Bloomberg, a gun control advocate, heard the familiar in Obama's initial response, despite the striking emotion.

"Not enough," Bloomberg said of Obama's words. "We have heard all the rhetoric before. What we have not seen is leadership — not from the White House and not from Congress. That must end today."

The Newtown shooter brought three guns into the school, and the weapons were registered to his slain mother, according to a law enforcement official who was not authorized to discuss information with reporters and spoke on condition of anonymity. The official said a Glock and a Sig Sauer, both pistols, and a .223-caliber Bushmaster rifle were found in the school after the attack, and a fourth weapon was recovered outside.

One certainty in the weeks to come is that both parties in Washington will carefully watch public opinion on gun control and the Second Amendment, and whether any impact lasts.

Opposition to stricter laws has proved resilient. Firearms are in one-third or more of households and suspicion runs deep of an overbearing government whenever it proposes expanding federal authority. The argument of gun-rights advocates that firearm ownership is a bedrock freedom as well as a necessary option for self-defense has proved persuasive enough to dampen political enthusiasm for substantial change.

In July, a gunman opened fire on Aurora, Colo., theatergoers watching the Batman movie, "The Dark Knight Rises," killing 12 people. The next month, an Associated Press-National Constitution Center poll found that 49 percent of Americans felt laws limiting gun ownership infringe on the right to bear arms, while only 43 percent said such laws do not infringe on those rights.

By many measures, Americans have changed on the question since the 1990s, when people favored gun control over gun rights — by a 2-to-1 margin in polling after the 1999 Columbine High School massacre in Colorado. In a Gallup poll last year, 55 percent said gun laws should stay the same or be more lenient, while 43 percent wanted them toughened.

None of this is lost on Washington, where most Democrats long ago abandoned their advocacy of gun control, convinced that it is a losing issue for them. Obama has proposed reinstituting a federal ban on military-style assault weapons that lapsed years ago, but he's put no weight behind it, while signing laws letting people carry concealed weapons in national parks and in checked bags on Amtrak trains.

After the movie-theater attack, Obama declared "we should leave no stone unturned" to keep young people safe in a speech indicating he would challenge Congress to act on gun control. That expectation lasted for one day. The White House swiftly clarified that Obama would not propose stiffer gun laws this election year and favored more effective enforcement of existing law — a position hardly distinguishable from that of his Republican rival, Mitt Romney.

Likewise, early last year, Obama weighed in on guns after an assailant killed six people and wounded 13, shooting then-Rep. Giffords in the head outside a grocery store in Tucson, Ariz. The president called for "sound and effective steps" in gun laws as part of a "new discussion on how we can keep America safe for all our people." He soon went back to silence on the topic and gun-control advocates waited in vain for the steps.

With his last presidential campaign behind him, Obama is freer to take up contentious matters that he wouldn't touch when he was an incumbent seeking re-election. Odds are favorable that he will have at least one vacancy to fill on a Supreme Court now closely divided on gun cases.

The Aurora attack happened in the heat of the campaign, when Democrats wanted no trouble from gun owners. In its first official response to the killings, Obama's White House pledged to protect fundamental gun rights. Obama and his spokesmen never failed to couple his wish for "common-sense measures" with his devotion to the Second Amendment.

But after the massacre of children Friday, Obama spoke mainly of the anguish, and the need for action, and not at all about the right to bear arms.

By the standards of gun-control politics, that alone was a crack in the status quo.

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Associated Press writer Matt Apuzzo in Newtown, Conn., contributed to this report.