While scholars disagree about whether and how much campaigns persuade voters, they increasingly agree that campaigns inform voters about the candidates and help voters bring their votes in line with their interests. Some argue that campaigns serve mostly to help voters bring their choices in line with preexisting political predispositions. This paper examines the crystallization of voter preferences during the 2008 presidential election campaign. The authors rely on polls from each month of the election year campaign to assess whether and how the structure of vote choice changed. The results show that certain election day predictors of the vote—especially party identification—became increasingly important predictors of preferences during the election cycle. Even the increase in party effects is mostly confined to the period leading up to the party conventions, well before the general election campaign even began. The structure of preferences evolved over the course of the long campaign.