Just outside the DC Beltway, in Maryland’s sprawling first congressional district, an electoral battle is underway that exposes unique ideological fault lines beneath America’s political landscape. The campaign pits freshman “Blue Dog” Democratic congressman Frank Kratovil in a rematch against Republican Dr. Andy Harris. Given the political tilt of the district, coupled with the Tea Party tsunami gathering force this year, one would think that this race should be a slam dunk for Harris. A tall, affable family man, Harris is an anesthesiologist, Navy veteran, hardcore free-marketer, and constitutional conservative. By contrast, Kratovil, a former attorney, tries to portray himself...