This paper argues that a model of sequential choice is superior to the standard rational choice model in explaining a process as complex and dynamic as the political realignment of the 1850s. Part 1 sketches the facts and processes that need to be encompassed by a model and identifies key branching points. Part 2 describes an appropriate model of sequential choice and discusses procedures for estimating transition probabilities and the impact of key variables on these transition probabilities. Part 3 identifies implicit assumptions of rational choice theory that limit its usefulness. Copyright 1992 Blackwell Publishers Ltd..