DUBUQUE — Inside Knicker’s Saloon, a factory worker hangout here, Jesse Oberbroeckling has just finished his shift at the John Deere plant when he reveals his regret.Like many union workers, Oberbroeckling voted twice for former Democratic President Barack Obama before backing Donald Trump and other Republicans in 2016.Now he has buyer’s remorse — and plans to support the Democratic challenger to Rod Blum, the Republican congressman in this blue-collar, Eastern Iowa district.“Trump is for the rich,” said Oberbroeckling, 37, sipping a rum-and-coke.