A hunter and lifetime member of the National Rifle Association, Democrat Joe Manchin won his Senate seat after airing an ad that showed him firing a rifle and shooting a hole in the cap-and-trade bill backed by President Obama. Now the West Virginia senator is the point man on Capitol Hill for reviving legislation on background checks for gun buyers that lawmakers killed just three weeks ago. With polls showing the public turning on some Republican senators who voted against the popular bill, Manchin’s crusade for a second wave of gun legislation could succeed.