CROSSOVER VOTING. It's been Instalanched, but read Citizen Smash's discovery of the requirement to declare a party identity in order to vote in the California primary. It is worth remembering that the primaries are primarily a party function, and citizens who skip the primaries are not presumptively derelict of their civic duties. The parties go to great length to prevent crossover voting, the phenomenon of voting for the candidate you least like in order to enhance the chances for the candidate you most like. The Making of the President 1960 (details or compare prices) has some rather colorful passages about the effects of crossover voting.