A considerable body of research focuses on why voter turnout changed - specically, why it declined - in the 1960s and 1970s. Most models of the change focus on factors such as a decline in civic involvement or a shift in the age distribution toward younger citizens who vote less frequently. While these approaches have taught us much about voter turnout, they are puzzling in that none actually focuses on the origins of change. That is, they explain changes in turnout with changes in other factors but never directly explain these other changes. Further- more, almost all existing models of voter turnout dynamics assume exogeneous party choices, although voters' party choices are not xed in general and this fact likely has consequences for voter turnout. I develop a model of turnout dynamics | one that directly explains changes in turnout | with endogeneous party choice. I show that this model explains voter turnout in U.S. presidential elections better than other models, and I reach similar results in the context of California voter registration data. While voter registration is of obvious importance to voter turnout, it receives little attention and its dynamics have never been studied
