Could shooting be a tipping point in gun-control debate?

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

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

But now? The massacre in Newtown, Connecticut - which took the lives of 20 children and six adults at the school, the gunman's mother at home, and the gunman himself - stands as a possible tipping point in Washington's decade-long aversion to even talking about stricter gun laws.

So it seems in the stunned aftermath, judging from US 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 the massacre at Sandy Hook Elementary School 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 is 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."

After the massacre of children on 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.