The Incumbency Effect in Congressional Elections: A Test of Two Explanations

TWo recent trends in American politics-a decline in the number of competitive congressional seats and an increase in the partisan independence of the electorate-originated in the mid-1960s and progressed at similar rates for the next decade. We tested the possibility of a causal relationship between these two phenomena and found, contrary to previous speculation and research, that partisan dealignment accounts for little of the increase in incumbency voting. Consequently, we suggest that the change in electoral fortunes of incumbent congressmen has been brought about mainly by congressmen themselves and not by exogenous changes in the electoral environment.