DES MOINES — J.D. Scholten has gotten phone calls from former U.S. Rep. Beto O’Rourke. He’s campaigned with U.S. Sen. Cory Booker. He held a town hall with entrepreneur Andrew Yang and toured an ethanol plant with U.S. Sen. Amy Klobuchar.The presidential candidates are eager to meet with Scholten, hoping he holds the key to a secret that bedevils Democrats: how to win rural voters, who seem to be firmly in President Donald Trump’s corner.Scholten, a former minor league baseball star, challenged GOP U.S.