DES MOINES, Iowa — There’s not even a kernel of hope for Mayor Bill de Blasio in this decidedly unscientific Iowa State Fair poll. Even after his food- and game-filled Sunday at the fair — where he gave a 20-minute pitch to voters at the famed Political Soapbox — the New York City mayor is registering at 0 percent in the fair’s corn kernel poll. Attendees at the fair over the age of 18 can place a kernel of corn into a jar to select their top caucus choice. Around 6 p.m. Sunday, after the mayor’s tour around the fairgrounds...