For a time in December, it looked as though the nation was finally ready to take on the gun culture. Perhaps you recall the moment: twenty grade-schoolers, along with their teachers and their principal, had been added to the roster of 30,000 people killed by guns in America each year. The details of the massacre were at once terrible and familiar — indeed, you could have guessed them as soon as you heard the first sketchy news bulletins. A murderer lost in some sanguinary fantasy. High-capacity magazines. In the starring role, one of our society’s prized slaughtering machines: an AR-15…