Mayor Pete Buttigieg and Gov. Steve Bullock on Tuesday night both spoke in stark terms about how the epidemic of gun violence had personally affected them.

During the Democratic presidential debate, Mr. Buttigieg, the 37-year-old mayor of South Bend, Ind., recalled being in high school when two students killed 12 classmates and a teacher at Columbine High School in Colorado in 1999.

“I was part of the first generation that saw routine school shootings,” Mr. Buttigieg said. “We have now produced the second school shooting generation in this country. We dare not allow there to be a third.”

[Highlights from Night 1 of the July Democratic debates]

Mr. Buttigieg, who supports universal background checks and banning assault weapons and has endorsed a national gun licensing program, described the difficulty he has faced in helping families who were victims of gun violence in his city.