SPRINGFIELD — Gov. J.B. Pritzker on Thursday said that Illinois House Speaker Michael J. Madigan should step down as chairman of the state Democratic Party, agreeing with the state’s senior U.S. senator that the longtime political powerbroker’s implication in a federal bribery investigation hurt Democrats in Tuesday’s elections.Pritzker made a more general statement on Wednesday that voters jaded by a spate of corruption involving Democrats had helped sink his administration’s top priority …