Explaining Patterns of Candidate Competition in Congressional Elections

The low probability of defeating incumbent members of Congress deters potentially strong rivals from challenging them. Yet almost all incumbents are challenged, usually by opponents who lack previous experience in office and run underfinanced, ineffectual campaigns. But if strong challengers are deterred from challenging incumbents, why are not weak challengers, who have even less chance of unseating an incumbent? The model developed in this paper indicates that there is a simple reason why weak candidates choose to run against incumbents: they do so in order to maximize their probability of getting elected to Congress. Together with the findings of previous researchers, the results of our analyses of congressional primary data from 1980 through 1984 provide strong support for the major hypotheses derived from our model.