By Steve Holland and Jeff Mason and Susan Cornwell
WASHINGTON (Reuters) - His words have been eloquent and sympathetic, as they typically are when he is the voice of a nation in mourning.
But President Barack Obama's response to a gunman's massacre of 20 children and six adults at a Connecticut grade school has revealed a more complex view of the president: emotional, frustrated - and perhaps rethinking his largely hands-off approach to gun control.
"We can't tolerate this anymore," Obama said late Sunday at the vigil for the victims in Newtown, Connecticut, as he recalled earlier mass slayings and the shooting of former U.S. congresswoman Gabrielle Giffords in 2011. "These tragedies must end. And to end them we must change."
Obama notably did not use the word "gun," but he did cast his argument against violence in terms of another politically potent image: protecting America's children.
"Can we honestly say we're doing enough to keep our children, all of them, safe from harm?" Obama asked. "...If we're honest with ourselves, the answer's no. We're not doing enough and we will have to change."
Obama promised that "in the coming weeks, I'll use whatever power this office holds to engage my fellow citizens - from law enforcement to mental health professionals to parents and educators - in an effort aimed at preventing more tragedies like this."
It was the strongest signal yet that Friday's shootings and Obama's standing -- he was just returned to office and will not be up for election again -- may have inspired him to embrace gun control as part of his second-term agenda.
It is an issue around which Obama has stepped carefully during his first term and his re-election campaign, to the frustration of gun-control advocates.
Despite a series of mass killings by gunmen in recent years, polls have long indicated that most Americans are wary of increased restrictions on guns.
And the gun lobby, led by the National Rifle Association, has been a powerful force in building support among Republicans and rural Democrats, to the extent that trying to push new gun limits through Congress has been seen as a futile exercise.
But the slayings in Newtown, Connecticut, have given new momentum to calls for more limits on guns, including the reinstatement of a ban on the sale of "assault" weapons such as the semiautomatic rifle that gunman Adam Lanza used.
Sen. Dianne Feinstein, a California Democrat, said Sunday on NBC's "Meet the Press" that she will introduce a proposed ban on assault weapon sales when the new Congress convenes in January.
New York Governor Andrew Cuomo, a potential Democratic contender for president in 2016, was among others calling for new laws that would limits access to guns.
And New York City Mayor Michael Bloomberg, a persistent and vocal voice for gun control, essentially warned Obama against inaction, saying that it should be at the top of his agenda.
It's unlikely that Obama will go that far, but it is clear that the Newtown shootings - and the fact that five of the 12 most deadly shootings in U.S. history have occurred since Obama took office in January 2009 - are weighing on the president.
"If you put aside the loss of troops ... these specific instances of the shootings have impacted him more personally than anything else," said one former Obama aide, speaking on condition of anonymity.
Even so, any effort to get a significant change in gun policy through Congress would be complicated by other legislative priorities Obama has for his second term, the former aide said.
"So the question is: Is (gun control) his thing? Or is it immigration or tax reform?" the former aide said, listing other policy goals. He said it was highly unlikely that the president could tackle all three.
WHAT IS 'MEANINGFUL ACTION'?
Whatever the obstacles, Obama effectively has committed himself to do something aimed at reducing gun violence by promising to take "meaningful action."
So after the emotion of the moment has subsided, what might he do?
Some analysts believe that Obama would support a renewed push by Democrats in Congress to reinstate the assault weapons ban, which Congress allowed to expire in 2004. The analysts also believe that he would back stronger steps to ensure that the mentally ill are unable to buy firearms easily.
Obama may be able to take some action by executive order, without waiting for Congress to act.
"We could do more to improve our mental health data reporting into the background check system," said Adam Winkler, a professor at the UCLA School of Law. "That may be done by executive order."
However, Winkler said, the Supreme Court has said that states can't be forced to hand over such data to the federal government. State objections to doing so often revolve around costs; Winkler suggested that more federal grants may be needed to serve as a financial incentive for states to report the data.
Winkler also said that the system now used to make sure gun buyers do not have criminal backgrounds should be improved, but that probably would require an act of Congress. Because of various loopholes, many lawful gun sales occur without any background check, Winkler said.
It isn't clear whether such changes could have prevented many of the shootings that have plagued the nation in recent years. In the Newtown case, for example, the three guns Lanza used in the shootings appear to have been purchased legally by his mother, who was Lanza's first victim, authorities said.
White House officials have not elaborated on what Obama meant by "meaningful action."
Bloomberg and other gun-control advocates say the president needs to move quickly and decisively, or risk being cast as part of the problem.
"We have heard all the rhetoric before," said Bloomberg, who endorsed Obama's re-election this year. "What we have not seen is leadership - not from the White House and not from Congress."
A CHANGING POSITION
Early in his political career, Obama expressed support for increased restrictions on guns.
As a state senator from Illinois representing an urban Chicago district in 2000, he was quoted in the Hyde Park Herald as calling for increased penalties for the use of guns, limiting buyers to one gun purchase a month and tougher laws to stop the sale of firearms at gun shows.
During his first campaign for president in 2008, Obama said he backed reinstating the assault weapons ban.
But once in office, he made no big push to do so, a stance that reflected a lack of enthusiasm on Capitol Hill for such legislation.
About a month after Obama took office, in February 2009, Attorney General Eric Holder said that the administration wanted to reinstate the ban on the sale of assault weapons.
But then House Speaker Nancy Pelosi of California, a fellow Democrat of Obama, threw cold water on the idea. "I think we need to enforce the laws we have right now," she said then.
And a spokesman for another Democratic leader, then-Senate Majority Leader Harry Reid, said the senator would oppose any effort to revive the assault weapons ban. Reid, a Democrat from the western state of Nevada, had voted against the ban when it was instituted back in 1994.
Holder then backtracked. When he was asked about the assault weapons ban again three weeks later, he said, "I think what we're going to do is try to enforce the laws that we have on the books."
Pelosi and Reid have not said whether they would embrace any new efforts to push for an assault weapons ban or other gun-control measures.
To date, Obama's administration actually has expanded gun rights: He signed a law allowing concealed guns to be carried in national parks such as Yellowstone and the Grand Canyon, and allowing guns in checked baggage on Amtrak trains.
The Brady Center to Prevent Gun Violence issued a scathing report in 2010, saying that Obama had "abdicated his responsibility" on the issue and giving him a grade of "F" for failing to support gun restrictions he had supported while campaigning.
A NEW 'POLITICAL CALCULUS'
But the Newtown shooting "may well be a turning point for the gun debate in America," said Winkler, author of "Gunfight: The Battle over the Right to Bear Arms in America."
"People seem angrier than ever before," he said. "To see 20 children mercilessly slaughtered in a schoolhouse is too much for people to bear. I think the political environment is different today than it was even a few weeks ago. President Obama, who has avoided gun control assiduously, no longer has to worry about re-election. President Obama didn't want to talk about guns, because a lot of swing-state voters feel very passionately about guns and he needed to win those votes."
Now, Winkler said, "his political calculus has got to be different."
Winkler also noted that several Republican congressional candidates who received more than $100,000 from the NRA for the November elections wound up losing. The NRA has not commented on the shootings.
"The NRA had a pretty rough November," Winkler said. "So maybe Democrats are not as fearful of electoral retribution by the NRA."
(This story has been refile to adjust headline)
(Mason reported from Newtown, Connecticut; Editing by David Lindsey and David Storey)