The National Rifle Association may be a nation unto itself in its commitment to the right to bear arms. The number of members attending its annual convention here is larger than the combined populations of Jeffersonville and Clarksville, Ind.; more than 70,000. But the message its leadership delivered by endorsing Donald Trump, and by hosting his second Louisville visit, is aimed at the more than 5 million members who stayed home. "This election is about the soul of the country, and the Second Amendment," said Chris Cox, executive director of the NRA's Institute for Legislative Action. "If your preferred candidate...