The mass killing on Friday at a Connecticut school put renewed pressure on U.S. President Barack Obama and other Democrats to reverse their years of caution about gun control laws and address the easy availability of firearms.
The scenes from Sandy Hook Elementary - of children running from a school where a lone gunman killed at least 20 children and six adults - were certain to stir public opinion, supporters of gun control said.
Just an hour after Obama tearfully said on national television that the country needs "meaningful action to prevent more tragedies," about 200 people rallied outside the White House on a cold evening in favor of gun restrictions.
Their hopes were buoyed by Obama's re-election last month, a development that could free the president - a longtime advocate for gun control - to approach the subject without fear of political consequences in his second four-year term.
However, Obama still faces a Republican-led House of Representatives that could block such reforms.
New York City Mayor Michael Bloomberg, who runs a coalition of mayors on gun policy, said Obama should not be deterred and should send legislation to Congress.
"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," Bloomberg said in a statement.
U.S. lawmakers have not approved a major new gun law since 1994, and they let a ban on certain semiautomatic rifles known as assault weapons expire in 2004.
FEAR OF NRA
Faced with intense lobbying by the National Rifle Association and other gun groups, and fearful of a backlash from gun-owning voters, most Democrats have stopped trying to pass new laws.
Their caution has continued despite high-profile incidents such as the January 2011 near-fatal shooting of Democratic Representative Gabrielle Giffords in Tucson, Arizona, and the July 2012 killing of 12 at a movie theater in Aurora, Colorado.
But, supporters of gun control said, two factors may shake Democrats out of their passive stance: the increasing frequency of mass killings, and the defenselessness of the young children killed at the school in Newtown, Connecticut.
Some gun rights supporters said after the Aurora massacre that the shooter might have been stopped if more theater-goers had been armed. But this argument is more difficult to make in the latest incident.
"You can't have an elementary school teacher have a gun in her purse. You just can't do that," said Josh Horwitz, executive director of the Coalition to Stop Gun Violence.
Outside the White House on Friday, the crowd held candles and chanted, "Today is the day." Some dabbed tears. People carried signs reading, "Too many guns" and "Disarm."
Anna Oman of Silver Spring, Maryland, was in the crowd with her 5-year-old son, Hugo.
"I felt today like I did on Sept. 11," she said. "I had to do something."
NRA spokesman Andrew Arulanandam said in an email: "Until the facts are thoroughly known, NRA will not have any comment."
The NRA's strength could be tested anew after its largely unsuccessful efforts in the 2012 election. The organization pushed strongly for Obama's defeat, and most of its favored candidates for the U.S. Senate lost.
Any national gun legislation would face its most difficult obstacle in the House, whose Republican leaders have strong ties to the NRA.
BOEHNER'S 'A' RATING
House Speaker John Boehner has received an "A" rating in the past from the NRA, the largest lobbying group for gun owners and makers. Boehner released a statement mourning the deaths in Connecticut, but the Republican leader would have no comment on possible gun control legislation, a spokesman said.
Another lawmaker with an "A" rating from the NRA, Virginia Republican Representative Bob Goodlatte, will have jurisdiction over gun bills when he starts next month as the new chairman of the House Judiciary Committee. A spokeswoman did not respond to a request for comment on Friday.
Mark Glaze, director of Bloomberg's group, Mayors Against Illegal Guns, said it would take presidential involvement for the issue to gain momentum.
"After Tucson, after Aurora, and now after Newtown, we've been told it's time for a moment of silence. And that moment of silence stretches into months. The president could actually make a difference, and it's time for him to try," Glaze said.
On social media, some people responded to the Connecticut shooting by trying to coin new terms to replace "gun control," such as "massacre prevention."
There is no shortage of ideas among gun control advocates.
They could push to require background checks for all gun purchases; checks are now required only at licensed commercial dealers but not among private sellers. They could also push for a federal law on gun trafficking, for tougher sentences for illegal purchases or for more resources for the U.S. Bureau of Alcohol, Tobacco, Firearms and Explosives.
U.S. Attorney General Eric Holder was in Connecticut this month to talk about guns - but only about gun violence among gangs, not gun control generally.
On Wednesday, a day after a shooting at an Oregon shopping mall, Holder told reporters that the Obama administration was in discussions about proposals but he made no commitments.
"There are a number of proposals that we're in the process of considering, and I expect that you will be hearing from the administration," Holder said.