As both major parties gear up for the big push toward November's midterm balloting, accusations are flying in many states and districts that one party or the other is recruiting phony candidates so as to distort voter turnout. The idea, most of the accusers allege, is to pick off favored opposition candidates by filling their primary slates with candidates who either poach from their voter base or sow confusion on the ballot, thereby producing a weaker nominee to run against in the general election. Last month, for example, Democrats cried foul over the outcome of the South Carolina primary vote,...