The partisan realignment of the White South, which transformed this region from being solidly Democratic to being the base of the Republican Party, has been the focus of much scholarship. Exactly how it occurred is unclear. Widespread individual-level attitude changes would be contrary to the well-known within-person stability of party identification. However, according to the impressionable-years hypothesis, events that occur during adolescence and early adulthood may have a lasting impact on later political attitudes. This would suggest that cohort replacement may be driving partisan realignment. We test this possibility using data from the American National Election Studies from 1960 to 2008. Consistent with the impressionable-years hypothesis, Southern Whites from the pre-Civil Rights cohort (born before 1936) maintained their Democratic Party identification longer than their younger counterparts. However, all cohorts in the South have changed their partisan attitudes at comparable rates over time, contrary to the impressionable-years hypothesis. These data suggest that the partisan realignment of the South was driven by both cohort replacement and within-cohort attitude change. More targeted case studies of older cohorts living through the civil rights era, and of younger cohorts in the post-Reagan era, yield results generally consistent with the impressionable-years hypothesis. More generally, our findings suggest that very large scale events are required to disrupt the normal continuity of party identification across the life span.