Ms. Sanders, her voice breaking at times, responded: “I think that as a kid, and certainly as a parent, there is nothing that could be more terrifying for a kid to go to school and not feel safe. So I’m sorry that you feel that way.”

She continued: “This administration takes it seriously, and the school safety commission that the president convened is meeting this week again, an official meeting, to discuss the best ways forward and how we can do every single thing within our power to protect kids in our schools, and to make them feel safe and make their parents feel good about dropping them off.”

President Trump has called for action after some high-profile school shootings, but little has come of it beyond the creation of the commission, which is overseen by Betsy DeVos, the education secretary.

After a shooting at Marjory Stoneman Douglas High School in Parkland, Fla., killed 17 people in February, Mr. Trump said he would look at stricter background checks and raising the minimum age for buying assault weapons. He also suggested arming teachers, giving them a bonus to carry guns.

Those proposals have gone nowhere. He later said on Twitter that there was “not much political support (to put it mildly)” on raising the minimum age.