Beginning with work by Robert Erickson in the early 1970's, there has been a substantial amount of research into the phenomenon known as incumbency advantage. There has also been a significant growth in the analysis of Congress based upon the rational choice model, using the desire for reelection as the basis for modelling congressional behavior. As always, there is an ongoing debate about the value of congressional output. To date, there has been no attempt to examine the impact of the growth of incumbency advantage upon congressional behavior. This paper attempts to measure the effects of incumbency, operationalized as tenure and winning margins, upon congressional behavior as reflected by voting scores complied by CQ over the post war period. If the rational choice model is correct, we expect to find that increased safety has led to less presidential support and less party unity. The mass of evidence presented here reveals no such pattern associated with increased margins or increased tenure.