In 1985, Barack Obama traveled halfway across the country to take a job that he didn't fully understand. But, while he knew little about his new vocation--community organizer--it still had a romantic ring, at least to his 24-year-old ears. With his old classmates from Columbia, he had talked frequently about political change. Now, he was moving to Chicago to put that talk into action. His 1995 memoir, Dreams from My Father, recounts his idealistic effusions: "Change won't come from the top, I would say. Change will come from a mobilized grass roots. That's what I'll do. I'll organize black folks....