Since the 2012 massacre at Sandy Hook Elementary in Connecticut, where a gunman killed 20 children and six staff members, there have been 142 school shootings in the U.S. That’s equal to a rate of one per week. Of those incidents, 62 took place on college campuses, including Thursday’s shooting at Umpqua Community College in southwest Oregon.

While details are still developing about how the gunman at Umpqua—who was one of the 10 killed—planned and executed his assault, one that’s emerged is that when he entered the college campus armed with six guns, it was within his legal rights to do so.

Oregon law allows the carrying of concealed weapons on public college campuses. That law is the result of a court decision in 2011 that kept public colleges from banning firearms on campus. Public schools can bar guns from specific settings—classrooms, dormitories, and sports stadiums—but not from the campus outright.

Oregon’s leniency toward guns on campus is relatively unique in the U.S. All but nine states either ban carrying a concealed weapon on a college campus or leave the decision to bar or allow on-campus firearms to the college or university, according to data collected by The Campaign to Keep Guns Off Campus, a group that aims to disarm schools.

Oregon—along with Arkansas, Colorado, Idaho, Kansas, Mississippi, Oregon, Utah, Texas, and Wisconsin—have provisions that allow the carrying of concealed weapons on public campuses. And this year, lawmakers in several states launched multiple efforts to follow suit.

In 2015, legislators in 15 states introduced 22 bills that called for a loosening of gun restrictions on college campuses, according to The Campaign to Keep Guns Off Campus. By comparison, there was just one bill introduced that would make it tougher to carry a firearm on a college campus. The measure, introduced in California, would prohibit any concealed carry permit holder from bringing a weapon on a public or private college campus without permission from campus officials. It passed both houses of the state legislature and was submitted to Governor Jerry Brown for signature in early September.

The pro-gun bills that state legislatures considered this year are indicative of a push by the gun lobby to open up another market of potential gun owners—college students. That’s very appealing to the industry’s biggest lobbying group, the National Rifle Association, and gun manufacturers, says Lindsay Nichols, a senior attorney at the Law Center to Prevent Gun Violence.

The NRA did not return Fortune‘s request for comment.

Despite the push for looser on-campus gun laws, all but one of the 22 pro-gun measures met defeat. Nichols says that’s attributable to “common sense that college campuses are not good places for guns” due to their “enclosed spaces” and populations of young people who are prone to using drugs and alcohol.

The one victory pro-gun advocates had was a sizable one. Texas became one of the nine states to allow firearms on college campuses in June when Governor Greg Abbott signed a “campus carry” law, which allows gun license holders to carry concealed handguns on public college campuses. Top universities in the state came out against the law, and opponents were able to secure some caveats. University presidents will be able to designate “gun-free zones,” but they can’t ban handguns on entire campuses.

Oregon’s law allowing firearms on campuses has faced its own challenges. A proposal to prohibit guns on school campuses was introduced in 2012, but it failed to pass the state Senate. (The following day, the state’s board of higher education adopted a policy that bans guns from some areas of campus—classrooms, dormitories, sporting arenas—at the state’s seven universities—but the measure doesn’t keep someone with a concealed weapon permit from walking across a state university campus with a gun.)

When the effort to ban firearms on Oregon campuses failed in 2012, State Senator Jeff Kruse, a Republican from Roseburg, where Umpqua Community College is located, acknowledged that violence in schools is an issue but said that the measure was “purely” political. He characterized the bill as a “solution in search of a problem.”