Numerous scholars have documented a dramatic increase in incumbency advantage in US congressional elections and also state legislative elections over the past four decades. For example, Gelman and King show that incumbents in the House of Representatives now receive about twelve extra percentage points solely as a result of holding congressional office during the campaign; the comparable figure for most of the first half of this century was only 2 per cent. This advantage of incumbency has made members of the US House and many state legislators nearly invulnerable to electoral defeat.
* Department of Government, Harvard University. Thanks to Mo Fiorina for helpful comments, Paul Brace for his data and the National Science Foundation for grant SES-89-09201.