The sight of the bodies of 20 small children lying on the floor of a first grade classroom in Newtown, Conn., rattled most Americans.
The carnage inside an Aurora, Colo., movie theater sickened even the most hardened of law enforcement personnel.
The story of a promising, young black girl cut down on a Chicago playground galvanized a city inured to gang violence.
But despite the violence and the rhetoric that followed, it remains unclear in the United States how to go about keeping guns out of the hands of those who should not have them.
Part of the problem is, though most people agree criminals and the mentally ill should not have access to weapons, little can be done about actually blocking the flow short of banning all weapons sales and confiscating the guns already out there.
President Barack Obama again laid out his case last week for taking steps to close loopholes that allow guns to get into the wrong hands.
"If you ask most Americans outside of Washington -- including many gun owners -- some of these ideas [for limiting gun sales], they don't consider them controversial," Obama said, flanked by, among others, the mother of Hadiya Pendleton, the 15-year-old who was shot to death in a Chicago park a week after she had participated in Obama's inaugural festivities in Washington. "Right now, 90 percent of Americans -- 90 percent -- support background checks that will keep criminals and people who have been found to be a danger to themselves or others from buying a gun. More than 80 percent of Republicans agree. More than 80 percent of gun owners agree. Think about that. How often do 90 percent of Americans agree on anything? It never happens.
"Many other reforms are supported by clear majorities of Americans. And I ask every American to find out where your member of Congress stands on these ideas. If they're not part of that 90 percent who agree that we should make it harder for a criminal or somebody with a severe mental illness to buy a gun, then you should ask them, why not? Why are you part of the 10 percent?"
Would background checks have prevented Adam Lanza from killing those children and six adults at Sandy Hook Elementary School in Newtown? No. The weapons were purchased legally by his mother, his first victim. So, unless the limits also apply to family members of the mentally ill, he still would have had access to the weapons.
Would they have prevented James Holmes from shooting up a midnight showing of "Batman: The Dark Knight Rises?" Maybe. He bought his arsenal on the Internet.
The legislation being considered in the U.S. Senate already has been stripped of two major provisions: a ban on further sales of military-style assault weapons and a ban on large-capacity magazines.
Wayne LaPierre, the point man for the National Rifle Association, said after the Newtown massacre the best way to prevent such incidents is for more people to be armed. At the recent Conservative Political Action Conference outside Washington, LaPierre charged expanded background checks would lead to a federal registry of gun owners.
The paranoid say such a registry would give a tyrannical government a list of who should be disarmed first. They say the whole gun control argument is just a cover for disarming the populace to give the government the upper hand, and there are those who assert gun control is a plot to make Americans defenseless against foreign attacks, perhaps by al-Qaida.
Television evangelist Pat Robertson, in an introduction to a report on bulk purchases of ammunition by the Department of Homeland Security, described "long trains full of armored vehicles, personnel carriers with armor, what are they for, the army going into battle against the enemy? They're used by Homeland Security against us."
"Imagine what Homeland Security is doing, it's just awful and we're going to talk about how much ammunition they're stockpiling," Robertson said. "Who are they going to shoot, us?"
Cook County (Ill.) Board President Toni Preckwinkle thought she had a plan for funding medical care for victims of gunshot wounds: a 5-cent a bullet tax coupled with a $25 tax on every gun purchase. Other county board commissioners shot down the bullet tax. Area gun dealers have taken aim in court to block the weapons tax.
Cook County Sheriff Tom Dart proposed every gun transaction be reported to law enforcement. That way, he said, if there is a straw purchaser buying weapons in great numbers to be resold to gang members, police will be alerted and have a better chance of tracking and intercepting the weapons. That proposal has gone nowhere.
A recent Pew Research Center study indicates nearly half of gun owners say they want their weapons for protection with fewer than a third saying their primary focus is hunting. The result is in sharp contrast to a 1999 study that indicated weapons were mainly for hunting and only a quarter of gun owners said they wanted guns for protection. The attitude also contrasts sharply with crime statistics since violent crime is down 48 percent since 1993 and the homicide rate has been cut in half.
Arthur L. Kellermann, in a Rand Corp. commentary, notes despite the perception guns serve as protection, people living in households with guns are more likely than the general population to get shot, and often the bad guys get to a homeowner's gun before the homeowner does.
"After matching households on the basis of victim age, gender, race, neighborhood and socioeconomic status, and further adjusting for a wide range of behavioral risk factors, we found that keeping a gun in the home didn't affect a family's risk of homicide at the hands of an intruder. However, the overall risk of homicide was nearly three times higher, mainly due to a higher risk of domestic homicide," Kellermann wrote.
"Unfortunately, public health research on this subject is often dismissed by gun rights activists because it contradicts the claim that firearms make people safer in their homes. The bottom line for would-be gun owners is this: A firearm that is kept loaded and readily available in the home for protection may also be reached by a curious child, an angry spouse or a depressed grandparent."
In his remarks last week, Obama said the time for platitudes is over.
"Tears aren't enough. Expressions of sympathy aren't enough. Speeches aren't enough. We've cried enough. We've known enough heartbreak. What we're proposing is not radical, it's not taking away anybody's gun rights. It's something that if we are serious, we will do," Obama said.
"Now is the time to turn that heartbreak into something real. It won't solve every problem. There will still be gun deaths. There will still be tragedies. There will still be violence. There will still be evil. But we can make a difference if not just the activists here on this stage but the general public -- including responsible gun owners -- say, you know what, we can do better than this. We can do better to make sure that fewer parents have to endure the pain of losing a child to an act of violence.
"That's what this is about."