The story of U.S. Rep. Jesse Jackson Jr.’s severely diminished prospects for becoming a real force in Chicago politics essentially begins and ends at 312, a restaurant across the street from City Hall. That’s where the Democratic congressman and a top aide sat at a sidewalk table on a sunny day in August 2005. They barely touched their lunches, working their cellphones for the latest news on then-Mayor Richard M. Daley’s announcement that federal agents had questioned him. Jackson ultimately balked at challenging Daley, but a little more than three years later, he was at 312 again. This time, the...