After this latest school shooting, things seem different. I have no idea if we’ll end up with meaningful bullet control (as Chris Rock would say), but the translation of grief, anger, and frustration into policy seems more likely this time, compared to previous mass shootings in recent years.

What’s special about this case? Some natural hypotheses:

– The event itself is particularly horrifying: an elementary school instead of a high school, more kids getting killed, and the killer using three guns that were just lying around the house.

– Cumulation: each new shooting is added on to what came before, eventually enough people become motivated to act.

– Political timing: no national election for 23 months, now is the time for politicians to act without fear of the gun lobby.

– Political alignment: the Republicans have had so much success getting gun voters to their side that Democrats now have nothing to lose politically by supporting gun restrictions. And, if the Democrats move to restrict guns, savvy Republicans can move toward the center on the issue, confident that their Democratic opposition won’t outflank them on the right.

– The pendulum: to put that last point another way, gun policy has swung so far to the right in recent years that the force of public opinion will tend to pull it back to the center. This latest shooting has given politicians a chance to realize this and act on it.

Beyond all these reasons, let me suggest another which arises from my preoccupation with political geography.

The shooting happened in Connecticut. When people get massacred in Colorado, Arizona, or western Virginia, that’s every bit as horrible, but I wonder if there is an implicit social contract: we recognize that people in the southern and western states have lots of guns, they demand to have lots of guns, and it will be hard to take these guns away. People in these states don’t seem to mind all the guns. So from the standpoint of a voter in the east coast, sure, a shooting in Colorado or western Virginia is terrible, but nothing can be done about it because the voters there don’t want to do anything. It’s sad, but there’s nothing that can be done.

But if there’s a school shooting in Connecticut, that’s another story. The citizens of New England have not agreed to be bathed in guns. Yes, I know the long history of gun manufacture in the northeast, Springfield rifles and Smith & Wesson and all the rest. But bringing semiautomatic weapons to school is another story. Or, perhaps more to the point, the most prominent Americans defending the use of semiautomatic weapons in schools—the people who wanted to make sure that people like Nancy Lanza had the right to own these guns—are not, by and large, anywhere near Connecticut.

So, for the parts of the country that are generally in favor of gun restrictions, this latest shooting is particularly disturbing because it represents the politicians of the south and west imposing their will on residents of the northeast.

So, from this perspective, I can see why the Connecticut school shooting is different and could motivate political efforts, in a way that shootings in Colorado and elsewhere did not.

[Cross-posted at The Monkey Cage]

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Andrew Gelman is a professor of statistics and political science and director of the Applied Statistics Center at Columbia University.