In the aftermath of the Dec. 14 massacre at Sandy Hook Elementary School in Newtown, Conn., the nation finds itself once again dealing with questions that are hard to answer (Why did it happen? Could it have been prevented?) and harder still to ignore (How many more mass killings will it take before something is done to de-escalate America's homegrown arms race?) Official messages of mourning and half-masted flags won't stop the carnage. Decisive action at all levels of government is long overdue.