An analysis of the changing social bases of America's political parties: 1952–2008

• The social bases of both the Republican and Democratic Party have changed considerably.
• The Democratic Party is benefitting from the support of several groups that are increasing in size.
• The Republican Party has remained competitive due to increasing group loyalty and turnout.
• Demographic changes will force the Republicans to incorporate new groups to remain competitive.

In this article I address two interrelated questions: have the group bases of the American political parties changed over time and what factors have lead to the observed changes? I determine social group memberships significantly influence individual partisanship with a multivariate analysis using 56 years of ANES data. I then measure how many votes each politically relevant social group contributed to the party coalitions in each presidential election from 1952 to 2008. I discuss how group contributions have changed over time and establish the demographic and behavioral causes of group contribution change. I find that the party coalitions have been restructured as a result of groups' changing voting behavior and the changing ratio of groups in the electorate.