A prayer vigil outside Emanuel African Methodist Episcopal Church in Charleston, S.C., Wednesday night. (David Goldman/AP)

Wednesday’s mass killing of nine people in the Emanuel African Methodist Episcopal Church in Charleston, S.C., by a lone gunman shocks the conscience of any sane person. Inexplicably, the man, identified by authorities as 21-year-old Dylann Storm Roof, sat in on a prayer service at the historic African American church for an hour before opening fire in a moment of mayhem that has been too often replicated previously. Yet the very fact of another awful act of gun violence helps to explain why nothing will change.

For nearly a century, changes in gun laws have been keyed to two sets of events: gun-related violence and assassinations. Widespread criminal violence in the early 1930s accelerated efforts to enact national gun regulations, culminating in the passage of the National Firearms Act, which restricted such weapons and accessories as sawed-off shotguns, machine guns and silencers. As if to punctuate the connection between the law and criminal violence, the NFA was signed into law on June 26, 1934. Bookending the signing was the killing of the notorious criminal duo Bonnie Parker and Clyde Barrow on May 23, and of uber-gangster John Dillinger on July 22.

The assassination of President John F. Kennedy in 1963 prompted congressional hearings on unregulated mail order sales of guns, among other issues (assassin Lee Harvey Oswald obtained his rifle through interstate mail using a false name). Five years later, the assassinations of the Rev. Martin Luther King Jr. and Sen. Robert F. Kennedy finally provided the impetus to enact the Gun Control Act of 1968.

In 1989, a drifter shot and killed five children and wounded 29 others at an elementary school in Stockton, Calif., using a Chinese-made AK-47 assault weapon before killing himself. The shock of that shooting was a key catalyst to the enactment of the Brady law in 1993, which established background checks for handgun purchases from licensed dealers, and the assault weapons ban in 1994. In April 1999, another senseless school killing at Columbine High School in Colorado prompted the U.S. Senate to enact new gun measures, although the effort stalled in the House of Representatives.

And most recently, the mass shooting at Sandy Hook Elementary School in December 2012 prompted President Obama to press Congress for new gun laws, only to see the measures fail in Senate floor votes. (Ironically, the effort was initially backed by the National Rifle Association, but the group reversed course when it took flak from gun rights zealots who accused the organization of selling out.)

[5 facts about violence at houses of worship in the U.S.]

As the arc of this narrative suggests, gun policy change has become progressively more difficult. There are several explanations for why.

First, while more Americans favor than oppose tougher laws that could actually have some effect on gun violence (such as uniform background checks), the issue sits far down the list of issue concerns for average voters. Senseless gun violence mobilizes the public and focuses outrage, but that effect doesn’t last long. As the public turns back to other concerns, the gun policy debate is yielded to those who most care about the issue — gun rights proponents.

Second, the country has, to some degree, become inured to gun violence. With each new mass shooting, the sense of horror erodes, and so does pressure on lawmakers. That in turn heightens feelings that nothing effective can be done.

Third, the gun lobby has scored great success in changing the narrative of the gun issue. Guns aren’t the problem, it is bad people who do bad things, they say; gun laws don’t work; and Second Amendment gun rights must be preserved and protected. Their success in advancing their arguments lies with the relative weakness of pro-gun control forces (although that may be changing), combined with the election of the most gun-friendly president in history, George W. Bush, during whose administration top NRA priorities became policy. That, in turn, lent unprecedented legitimacy to gun rights arguments.

To be sure, none of those pro-gun propositions withstands scrutiny. While many products can cause injury and death, firearms are uniquely efficient and effective tools for killing. As criminologist Philip Cook has noted, guns don’t kill, they just make it much easier. Gun laws do work if we want them to — the 1934 gun law has been remarkably successful in keeping fully automatic weapons out of the hands of criminals, for example. And as the Supreme Court and our own history make clear, gun laws are perfectly compatible with gun rights. Indeed, for most of American history, guns were much more heavily regulated by the states than in recent years.

Finally, let’s note that gun laws are no panacea. Violence does have multiple causes, and people intent on mass violence can find many ways to carry out their perverse preferences. But elementary measures relating to firearms including better record-keeping, uniform background checks and restrictions on great firepower all find overwhelming support in the public at large, and among most gun owners. And there is good reason to believe that such steps would indeed help stem gun violence. In the current environment, however, such steps continue to be little more than political pipe dreams.