Ting Shen for The New York Times DES MOINES — Like many people in Iowa, Brianne Pfannenstiel has had campaign volunteers knocking on her front door. Unlike her neighbors, she must turn them away. That is because Ms. Pfannenstiel, 31, has a unique job: chief politics reporter at The Des Moines Register, the biggest newspaper in a state whose first-in-the-nation nominating contests give it an outsize role in picking presidents. She was once the […]