After Adam Lanza shot and killed 20 children and six adults at the Sandy Hook Elementary School in Newtown, Connecticut in 2012, activists may have thought that gun control at the federal level was a sure bet. But as the old saying goes, “there’s strength in numbers,” and the size of National Rifle Association’s membership has long outnumbered that of America’s gun reform groups. Leslie Crutchfield, the executive director of Georgetown University’s Global Social Enterprise Initiative, says high membership numbers is a matter of strategy. It doesn’t matter if the message is pro-Second Amendment, pro-gay marriage or anti-smoking. Those who know how to play the game get results. We talk to Crutchfield, who outlines social movement strategy in her new book,  “How Change Happens: Why Some Social Movements Succeed While Others Don’t.”