Rarely in my lifetime have I seen the type of civic engagement schoolchildren and their supporters demonstrated in Washington and other major cities throughout the country this past Saturday. These demonstrations demand our respect. They reveal the broad public support for legislation to minimize the risk of mass killings of schoolchildren and others in our society. That support is a clear sign to lawmakers to enact legislation prohibiting civilian ownership of semiautomatic weapons, increasing the minimum age to buy a gun from 18 to 21 years old, and establishing more comprehensive background checks on all purchasers of firearms. But the...