On Sunday night, President Obama spoke at an interfaith service for the victims of the horrific elementary school shooting. Not surprisingly, it was a poignant and moving speech. But the sad, horrible, tragic fact is that none of what we are witnessing is surprising. Shocking, yes, but not surprising. Mass shootings have become a defining feature of modern America. Yet on the issue of gun violence, President Obama has shown a gift for eloquent rhetoric but no follow-through. What we need now is not another national conversation but action -- starting with a ban on the sale of weapons that are only good for mass murder. Will the president lead the way? Will Congress act? Or will we succumb to the fatalistic conventional wisdom that says we'll never be able to prevent this from happening again -- and again and again?