Explaining the Ideological Polarization of the Congressional Parties Since the 1970s

Abstract:     
I trace out the etiology of partisan polarization of the House and Senate since the 1970s through an examination of exogenous and endogenous sources of trends in members' DW-Nominate and adjusted ADA Scores. I find that the increase in polarization is strongly related to the growing differences between the two parties' respective electoral coalitions and that the electoral connection works through adaptation (members adjusting their roll-call voting patterns to changes in their electoral constituencies) as well as through selection (replacement of more moderate with more extreme members). But the widening gap between the parties in the House and Senate cannot be explained by electoral forces alone, suggesting that events and developments endogenous to Congress - specific disputes, rules manipulated to partisan ends, slash-and-burn tactics of disgruntled minorities, and the strengthened hand of party leaders - have also contributed substantially to the trend.

working papers series