Interest groups and the electoral control of politicians

We develop a model of interest group influence in the presence of repeated electoral competition. In each period of the game, an interest group attempts to "buy" an incumbent's policy choice, and a voter chooses whether to replace the incumbent with an unknown challenger. The voter faces a tension between retaining good politician types and rewarding past performance. The model predicts that "above average" incumbents face little discipline, but others are disciplined increasingly - and re-elected at a higher rate - as the interest group becomes more extreme. Extensions of the model consider term limits, long-lived groups, and multiple groups.