The United States has scores of potential issues and ideologies but only two major political parties. How parties respond to competing demands for their attention is therefore central to American democracy. First to the Party argues that organized groups set party agendas by invading party nominations to support candidates committed to their interests. Where the nominees then go, the parties also go.

Using in-depth archival research and interviews with activists, Christopher Baylor applies this proposition to the two most important party transformations of the twentieth...