The Rev. Jesse Jackson Sr., who was diagnosed with Parkinson’s disease eight years ago, is stepping down from the Rainbow/PUSH Coalition, the influential Chicago-based civil rights organization he founded through its predecessor, Operation PUSH, more than 50 years ago. After ceding day-to-day operations last year, Jackson, 81, is formally handing the reins to his successor, the Rev. Frederick Douglass Haynes III, a senior pastor of friendship at West Baptist Church in Dallas. Haynes’ appointment is expected to be announced this weekend at the annual Rainbow/PUSH convention, sources said Friday. Haynes said it’s an honor to be chosen for this role....