The Case of the Vanishing Moderates
19
blocks to understand the mechanisms responsible for party polarization.
20
Regrettably, in politics and
most other questions of relevance in today’s world, there rarely is a smoking gun that can explain
everything. Rather, most right answers have the flavor of “a little of this” or “a bit of that.” The
bureaucracy, redistricting, a weakening of parties, and members’ personal empires all had a role in
the “Case of the Vanishing Marginals.” In the case of the vanishing moderates, the answer of “both”
seems right. The parties in Congress have become more polarized through both adaptation and
replacement.
Although figures 1 and 2 show a systematic trend toward polarization, are they simply
showing a magnification of a miniscule congressional trend? After all, an average change of 0.01 in a
member’s ideology score is negligible. Am I (and the other scholars studying polarization) making a
mountain out of a molehill? Has this study contributed to an intense examination of a trend that only
appears big when its historical context is ignored? In other words, are the continuous replacements
and adaptations like the grains of sand comprising a molehill or are they the big boulders comprising
a mountain?
One way to ascertain the magnitude of the trend is to compare the last congress in this study
(the 106
th
Congress in 1999-2000) to the first one (the 92
nd
Congress in 1971-2). If every member
and senator from the 92
nd
Congress had voted perfectly ideologically (i.e., every Democrat voting
against every Republican) in the 93
rd
Congress, the polarization score would have been 319.42 for the
House and 77.83 for the Senate (instead of 0.30 in the Senate and 1.67 in the House). In the 106
th
Congress, if every member and senator had voted perfectly ideologically, the total possible
polarization scores would have been 242.48 and 58.22. The total possible polarization score is lower
in the 106
th
Congress because the members and senators serving then were more polarized than their
colleagues from a generation before. The reduction from the 319.42 to 242.48 (77.83 to 58.22)
20
Various scholars, including Fiorina (1999), Lowry and Shipan (2002), and Poole and Rosenthal (1984) have
offered more comprehensive explanations for party polarization; however, their explanations can be broken
down pretty easily into the institution-based and districting-based categories.
Convention