In July 2014, Tennessee allowed residents to keep loaded weapons in their vehicles even without a concealed carry permit.

Wisconsin did away with its 48-hour waiting period for handgun purchases in June 2015.

Texas allowed students over age 21 to carry guns almost anywhere onto a university campus beginning in August 2016. (Sports stadiums are exempted, however.)

Florida, in February 2017, dramatically expanded its “stand your ground” law. Previously, the gun owner was required to prove that he or she had acted reasonably. Now Florida puts the onus on prosecutors to prove beyond a reasonable doubt that the gun owner acted unreasonably.

Effective June 2017, the state of Ohio allowed concealed-carry weapons to be brought into daycare centers and airports.

In July 2017, a local version of Florida’s “stand your ground” law took effect in Iowa, authorizing deadly force by gun owners. It also allowed gun use by children under 14, so long as they were under adult supervision, and extended concealed carry permits’ duration from one year to five.

Even more radical bills are in progress everywhere, too many to tally. Here’s just one example: Nevada, site of this week’s deadly massacre, took up in 2015 a law that would authorize gun owners to kill people they caught trying to steal their cars or motorbikes.

So it’s not at all true that “nothing changes.” In fact, a remarkable research paper published in 2016 by Harvard’s Michael Luca, Deepak Malhotra, and Christopher Poliquin found that between 1989 and 2014, the most probable policy response to a mass shooting was a loosening of gun laws.

A mass shooting increases the number of enacted laws that loosen gun restrictions by 75 percent in states with Republican-controlled legislatures. We find no significant effect of mass shootings on laws enacted when there is a Democrat-controlled legislature.

This may explain why gun advocates insist that the immediate aftermath of a spectacular massacre is “too soon” for the gun discussion. They want the pain and grief and fear to ebb. They want ordinary citizens to look away. Then, when things are quiet, the gun advocates will go to work, to bring more guns to places where alcohol is served, where children are cared for, where students are taught, where God is worshipped. More killings bring more guns. More guns do more killing. It’s a cycle the nation has endured for a long time, and there is little reason to hope that the atrocity in Las Vegas will check or reverse it.