Uvalde. Buffalo. Boulder. El Paso. Santa Fe. Parkland. Sadly, we know the names of these cities all too well – home to six of the nine deadliest U.S. mass shootings over the past five years. All carried out by people age 21 or younger . Mass acts of hate-based violence have become such a national issue that the White House is hosting a summit Thursday to counter their corrosive effects on our democracy and public safety.