Objectives. Building on work noting the difference between ambivalence and indifference, and long-standing theories of partisanship, this article seeks to examine the extent to which ambivalence and indifference differ in their impact on the likelihood of individuals defecting from their party when voting. Methods. Examining two national surveys, the voting behavior of ambivalent, indifferent, and one-sided individuals are compared. Results. It is shown that indifferent individuals are the most likely to defect from their partisanship and vote for the other major party or a third party and one-sided the least. Conclusion. Those who are indifferent toward the parties are distinct from those with one-sided or ambivalent evaluations, and this difference leads to a greater likelihood of voting against one's party in presidential elections.From the earliest studies of voting behavior, it was recognized that consistent partisans might behave differently than those facing internal and external conflict (Berelson, Lazarsfeld, and McPhee, 1954;Campbell et al., 1960). More recently, a great deal of attention has been paid to attitudinal ambivalence and its influence on political attitudes and behavior (e.g., Alvarez and Brehm, 2002;Feldman and Zaller, 1992;Basinger and Lavine, 2005). It has also been argued that some individuals are neither primarily one-sided nor ambivalent, but rather are indifferent (e.g., Meffert, Guge, and Lodge, 2004;Rudolph, 2005;Yoo, 2010). Such individuals have no meaningful reaction to the object in question, which in this case implies only a nominal attachment to either party. With less of a cognitive or emotional tie, I argue indifferent partisans are more likely than ambivalent and one-sided partisans to vote contrary to their partisan identity. Ambivalent partisans should be somewhat less likely to defect and one-sided the least.