Mayor Rahm Emanuel this week resurrected the idea of a high-speed rail system from downtown to O’Hare International Airport, a lofty goal that remained out of reach to his predecessor, former Mayor Richard M. Daley, who sunk $200 million into building a downtown station that never opened. Can Emanuel succeed where Daley couldn’t? The city is accepting proposals from developers, and billionaire inventor Elon Musk said he plans on bidding for the project.