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Introduction
David Rohde’s influential book Parties and Leaders in the Post-Reform House (1991) identifies a
sharp increase in Congressional party voting beginning in the late 1970s. Over the decade following
publication of this work, multiple explanations of the sources of increased party polarization emerged: (1)
the changing constituency bases of the parties (see, e.g. Rohde 1991; Black and Black 2002; Stonecash,
Brewer, and Mariani 2002; DiMaggio, Evans, and Bryson 1996), including the impact of changing levels
of income inequality on partisanship (McCarty, Poole, and Rosenthal 2002); (2) redistricting (Cox and
Katz 2002; Carson et al. 2003); (3) changes in voting procedures (Roberts and Smith 2003); and (4)
conversion (Theriault 2003; Carson et al. 2003). Fiorina (2001) provides an excellent summary of the
theoretical and empirical research exploring recent congressional party polarization.
In this paper, we put forward a separate perspective that builds on existing research, particularly
arguments focused on the changing constituency bases of the parties and the impact of reapportionment
on partisanship.
1
Our argument begins by redefining the time frame over which polarization occurs. The
prevailing assumption is that the recent period of polarization is unique and needs to be explained as such.
A closer look at historical data, however, shows that the recent period is instead a readjustment to pre-
existing patterns of polarization. Figure 1 presents Eric Schickler’s (2000) graphing of floor and party
medians in Congress (using DW-Nominate scores) .
[INSERT FIGURE 1 ABOUT HERE]
The most striking point of the graph is that the post-WWII period is, in fact, the unusual historical period.
The mean difference between the parties is at its lowest during this period and the polarization that
follows it is distinct only in comparison to the post-WWII period.
We argue that parties—in the electorate and in Congress—were closer than ever before in the
immediate post-WWII era because the class-based New Deal era was fading as the American economy
1
Our argument is also compatible with Roberts and Smith (2003), which argues that the rise in party voting
observed in the late 1970s is a result of changing voting roles and Committee of the Whole (COW) votes. They
argue that the “real” rise in polarization does not occur until the late 1980s. We return to this point later in the
paper.
Convention