For a brief moment in 2012, it seemed like a national stalemate over guns was breaking.
Adam Lanza, a 20-year-old gunman, had forced his way into a Connecticut elementary school and massacred 26 people, mostly children, with an AR-15-style rifle. Flags flew at half-staff. A sporting goods chain suspended sales of similar weapons. And longtime gun-rights supporters from both parties in Congress said they were willing to consider new legislation. The issue was complex, then-President