Attendees visit a booth at the 144th National Rifle Association (NRA) Annual Meetings and Exhibits at the Music City Center in Nashville, Tennessee, U.S., on Friday, April 10, 2015. Top Republican contenders for their party's 2016 presidential nomination are lining up to speak at the annual NRA event, except New Jersey Governor Chris Christie and Kentucky Senator Rand Paul who were snubbed by the country's largest and most powerful gun lobby. Photographer: Daniel Acker/Bloomberg via Getty Images
