While few would disagree that polarization in the US Congress has increased, there is much less consensus on the causes of this phenomenon. In a landmark study published in Econometrica, one of the most prestigious journals in Economics, Professor Canen and his coauthors (Chad Kendall, University of Southern California, and Francesco Trebbi, University of British Columbia) show that some of this increase may have little to do with politicians’ or voters’ changing ideology, and may instead be due to the internal organization of the two major American parties.
Over time, parties have become better able to discipline their members and make them toe the party line. Professor Canen’s work shows that party control accounts for a large fraction – approximately 40% - of the extent of political polarization. Put it differently, if party leaderships exerted no control over their members, Democrats and Republicans in Congress would behave much more similarly to each-other.
“Whips” are the main instrument of party control and are designated party members who mobilize votes among their representatives on major issues. Whips communicate the leadership’s position to party members, and conduct “whip counts,” polling members about how they plan to vote on major legislations. Through the whips, the party leadership can put pressure on individual representatives to conform to the party line.
Professor Canen and his coauthors show that, without the whip system, several major pieces of legislation would have either not passed or would have passed with much less support. In their period of study, this includes the 1983 Social Security Amendments and the 1984 Reagan tax reform. Parties also appear to take their ability to whip into account when introducing bills. Without the possibility of whipping, the authors find that the set of bills introduced to Congress would also be different.
Polarization, it seems, is a complex phenomenon. Beyond representatives’ ideological positions, it is shaped by political institutions, including the manner in which American parties are organized and managed by their leadership.