The story of Chicago gangsters in the 1920s is legendary. Less talked about is the tale of the politicians who allowed those gangsters to thrive. During the heyday of organized crime in the Prohibition era, Chicago mayor "Big Bill" Thompson and Gov. Len Small were the two most powerful political figures in Illinois. Thompson campaigned on making Chicago "a wide open town" for bootleggers. Small sold thousands of pardons and paroles to criminals, embezzled...