(The Center Square) – Amid concerns of President Joe Biden’s fitness to serve another four years in office, an Illinois congressman says he should step down. But a delegate says the party must unite ahead of the convention. Speaking with MSNBC Friday, Illinois U.S. Rep. Mike Quigley said Biden should secure his legacy. “The only thing that you can do now to cement that for all time and to prevent utter catastrophe is to step down and let somebody else do this,” Quigley said. Biden has been adamant he is remaining in the race. In a letter to Democrats Monday, he urged them to drop their concern…