LOS ANGELES — When Gov. Jerry Brown of California signed legislation this month banning concealed weapons on school campuses, the nation was in the midst of one of the worst spasms of gun violence at colleges in recent years. There were three such shootings, including one in Oregon that left 10 people dead, as the bill sat on Mr. Brown's desk.
But the new California law went against the grain of what lawmakers in many other states have sought to do. Over the past two years, nearly 15 states have debated legislation to make it easier for teachers, students and administrators to carry concealed weapons on campus. Supporters say the best way to subdue a campus assailant is ensuring that certain people on the scene can mount an armed response before the police arrive.
In June, Texas lawmakers made carrying a concealed weapon on campus legal as of August 2016. Similar measures are being debated in Florida, Ohio and Michigan. Last week, Wisconsin Republicans, who control the Legislature, introduced a bill that would ease restrictions on guns on campuses; two days later, Democrats countered with legislation banning guns on campus.
The issue has resonated on college campuses: At the University of Texas at Austin, students and faculty members have staged a variety of protests about the notion of guns on campus, and a professor announced he would resign, saying he would not feel safe in his classroom. In Florida, the state chapter of Students for Concealed Carry has been awarding free holsters to people who posted their support for that state's proposed legislation on Facebook. On some campuses, the argument has been made that arming students can help prevent sexual assaults.
Backers of the California bill, which passed with overwhelming Democratic support in both houses, predicted that the latest campus shootings would result in a rush across the country to pass measures banning guns in schools. Putting more guns on campus, they said, could confuse the police arriving on the scene about which armed person is the assailant and potentially result in more carnage during a cross-fire.
"The sentiment behind this law is our strong belief that law enforcement truly are the ones who need to be in control of arms on the campus," said State Senator Lois Wolk, the California Democrat who sponsored the bill. "And they are the only ones on campus that should be armed."
But in many places, people express the opposite view. In Oregon, after the shooting at a community college in Roseburg this month, people who live near the campus argued that the death count would have been lower if someone in the classroom had had a gun, and President Obama was jeered when he arrived there to visit victims' families, something many residents interpreted as part of his push for increased gun control.
"All of these shootings occur in gun-free zones," said Greg Steube, a Republican member of the Florida House and author of the proposed legislation there allowing guns on campuses. "Gun-free zones don't protect innocent people from a criminal walking onto a campus and shooting people."
Assemblywoman Shannon Grove, a California Republican who says she has a permit to carry a concealed weapon, voted against the bill in her state. "If you put up signs saying, 'No guns allowed on campus,' that's not going to stop people who are going to do you harm," Ms. Grove said in an interview. "And it's a really bad idea to stop qualified individuals from being able to carry their weapons in self-defense or in the defense of others."
The issue remains highly divisive, as has become clear in Texas, the state that most recently passed legislation allowing concealed weapons on campus. The measure is to take effect next Aug. 1, the 50th anniversary of the day an assailant fatally shot 14 people at the University of Texas at Austin, the first massacre on a campus.
To protest the law, opponents have swarmed the steps of university buildings, wearing orange shirts that read, "Gun Free UT" and "Armed with Reason." About 750 faculty members signed a petition stating their opposition to guns in their classrooms.
One economics professor, Daniel Hamermesh, resigned in protest over the law, saying he would not feel comfortable teaching in a classroom where there might be armed students. Joan Neuberger, a professor of Russian culture, said an increase in guns could lead to accidental injuries, suicides and a culture of fear in classrooms.
"In volatile situations like a mass shooting it's really, really unlikely that a 21-year-old with a gun is going to have an impact," Professor Neuberger said.
In Florida, where legislators have proposed a gun-friendly bill similar to the one in Texas, a gun rights group called Florida Carry filed suit against Florida State University last month after Rebekah Hargrove, a graduate student there, was barred from having a gun in her car during a school football game.
"Obviously, the 'gun-free zones' didn't work," said Ms. Hargrove, who leads the state's chapter of Students for Concealed Carry. She said she began supporting the right to carry weapons on campus after a man opened fire in the library at her school in November 2014, wounding three people. She added: "We trust our citizens to carry everywhere else. Why wouldn't we trust them to carry on campus?"
Some of the strongest opponents of laws allowing guns on campus have been university officials. The chancellor of the 15-campus University of Texas System, William H. McRaven — once a member of the Navy SEALs — said he did not think it would make students safer.
The campus police at the University of Wisconsin-Madison issued a statement last week calling on legislators to reject a proposal to allow guns in campus facilities, including the football stadium. Under a state law passed in 2011, guns are allowed on campus grounds, but the administration may ban them inside buildings.
Madison Laning, 20, the head of the student body government there, came out against the proposed legislation, warning that it would ultimately make things worse. "If — and hopefully never — we do have an active shooter on campus, it will make the PD's job so much harder," she said, referring to the Police Department, "if there are multiple people running around with guns trying to find the shooter."
Most legislatures are out of session now, so it may not be clear until next year if the recent spate of shootings — one person killed at Northern Arizona University, one at Texas Southern University and the 10 at Umpqua Community College in Oregon, including the gunman — will produce any change in weapons policy. These laws take many shapes. Some allow guns on campus but permit administrators to create specific restrictions — barring firearms from dorms or stadiums, for example. Other laws do not allow officials to create any gun restrictions. The California law applies to all schools.
"We will see in 2016 what states are going to do in response to these college and university shootings," said Allison Anderman, a staff attorney with the Law Center to Prevent Gun Violence. "Michigan is a red state. Ohio is a red state. So they are more likely to be moving this kind of legislation."
The number of states allowing students to carry firearms on campus has climbed since the shooting deaths of 33 people at Virginia Tech in 2007.
Ten states allow at least some civilians to carry concealed weapons on college campuses, either because of legislation or a court decision, according to the National Conference of State Legislatures.
At the time of the Virginia Tech massacre, "campus carry was considered one of these very rash ideas that was simply not acceptable to a majority of people," said Reid Smith, 28, a member of Students for Concealed Carry, which formed after that attack. "And that's changed a lot in the last seven, eight years."
California, where the governor is a Democrat and a gun owner, had among the toughest gun control laws in the nation even before the latest bill was signed.
"California is the only state that I know of that has passed a modern ban on people being able to carry a gun on college campuses," said John Lott, the head of the Crime Prevention Research Center, who testified last week in favor of the Michigan bill to permit concealed guns on campus. "The California law is interesting in that, can you point to one example of any problem they've had with the current rules? So why are they changing it?"
Since 2007, Idaho, Kansas, Mississippi and Wisconsin, as well as Texas, have passed laws that allow or will allow licensed gun owners to carry firearms on campus. Courts in Colorado and Oregon affirmed the right to carry guns on campus.
"Over the past three years, we have seen 12 to 20 states introduce legislation every session to allow guns on campus," said Suzanne Hultin of the National Conference of State Legislatures. "And every year, one or two states enact that legislation."