Why is it so easy to get guns in America? Cho Seung Hui purchased one of the pistols he used to shoot 50 of his classmates at a shop after showing an identity card and passing an instant background check. He appears to have got the other handgun he used legally as well. In Virginia, where his killing spree took place, guns are about as difficult to come by as Mexican food in Mexico.

School shootings are a regular occurrence in the US. Every one of them underscores the obvious point that guns should be harder to obtain. So does America’s death rate from firearm suicides, homicides and accidents, which is double or treble that of other developed countries. But, at least until this week, gun control simply had fallen off the national agenda. The assault weapons ban that Bill Clinton signed in 1994 expired in 2004. Even most Democrats have avoided the question of renewing it. Only in big cities have politicians not quite given up on the issue.