Shortly after the school shooting in Parkland, Fla., President Trump said that violent video games and movies may play a role in school shootings, a claim that has been made — and rejected — many times since the increase in such attacks in the past two decades.

Movies are “so violent,” Mr. Trump said at a meeting on school safety on Feb. 22, a week after the massacre at Marjory Stoneman Douglas High School, where, the authorities say, a former student, Nikolas Cruz, killed 17 people with a semiautomatic rifle. A neighbor of Mr. Cruz’s told The Miami Herald that he played video games, often violent ones, for up to 15 hours a day.

“We have to look at the internet because a lot of bad things are happening to young kids and young minds and their minds are being formed,” Mr. Trump said at the gathering of lawmakers at the White House, “and we have to do something about maybe what they’re seeing and how they’re seeing it. And also video games. I’m hearing more and more people say the level of violence on video games is really shaping young people’s thoughts.”

“And then you go the further step and that’s the movies,” he added. “You see these movies, they’re so violent, and yet a kid is able to see the movie if sex isn’t involved, but killing is involved.”