WASHINGTON – It’s been 11 years now – to the day – since most Americans learned how easily a person could use an AR-15 assault rifle to kill20 six- and seven-year-olds, along with six adults, at Sandy Hook Elementary School in Newtown, Conn. Hundreds more mass shootings have followed — at churches, concerts, shopping centers, supermarkets and, of course, many other schools. A commonality: sociopathic killers often choose AR-15s over less efficient killing machines. While the sorrow remains real and raw, the politics of guns have only grown more heated, divisive and partisan in recent years. Th…