Congressional incumbents are successful in over 90 percent of their reelection contests. Once explanation for this incumbency advantage is that incumbents provide services to constituents and interest groups as a means of generating both campaign contributions and votes. The model considered characterizes an electoral equilibrium in which candidates promise to provide services to interest groups in exchange for campaign contributions that are used to increase their probability of winning. Three explanations for the incumbency advantage result: a recognition advantage, a high personal valuation of the office, and an incumbent’s lower marginal cost of providing services. The model yields predictions that are consistent with empirical findings on campaign contributions and election outcomes.