Interest groups are introduced in a spatial model of electoral competition between two political parties. We show that, by coordinating voting behavior,these interest groups increase the winning set, which is defined as the set of policy platforms for the challenger that will defeat the...

Interest groups are introduced in a spatial model of electoral competition between two political parties. We show that the presence of these interest groups increases the winning set, which is the set of policy platforms for the challenger that will defeat the incumbent. Therefore interest...