VANDERBILT POLITICAL REVIEW
FEATURE
graph of nine-margin relative vote frequencies has some dramatic swings, the
overall trend is unquestionably upward,
making it reasonable to hypothesize
that at some point in the coming decades, unanimous decisions may make
up the majority (as opposed to simply
a plurality) of the court’s decisions.
Though this increasing number of
unanimous decisions could be due to
many factors – such as the changing nature of cases over the years – it is reasonable to assume that the final outcomes of
these cases would have been unchanged
even with a slightly different makeup of
justices. Instead, it is cases that were decided by a vote margin of one that are
of greatest concern; after all, many of
these cases could potentially have had a
completely different ruling (and resulting precedent) if a different party had
appointed just one justice on the court –
a reality that compromises the ideal of
depoliticized impartiality the Supreme
Court seems designed to promote. The
relative frequency of one-vote margins
has increased over time just as the relative frequency of nine-vote margins has,
from 11.1% of all decisions in 1974 to a
high of 32.0% in 2006 and back to 27.8%
in 2012. Thus, those lamenting increasing political polarization perhaps do have
some empirical evidence to back up their
claims; the relative frequency of onevote margins has almost tripled in the last
forty years. Nonetheless, it is important
to recognize that over seventy percent of
today’s cases are not decided in this way.
Even if there is some evidence of increased polarization in today’s Supreme
Court, it may not be nearly as problematic as some might claim insofar as these
extremely polarized cases represent a
distinct minority of all cases decided.
views and who will support their political agenda. As such, it seems reasonable to assume that justices chosen by
presidents of the same political party
would often vote together because of
similar ideologies and worldviews. With
this background in mind, we calculated
an “expected” vote margin for every
Supreme Court term between 1974 and
2012, and compared these expected margins to the actual average vote margins
observed during the same period. As
evidenced by the graph on the following page (Figure 3), the expected vote
margins and actual vote margins largely
match from 1975 through 1990 – a period beginning with the retirement of Justice William Douglas and his replacement by Justice John Stevens. It was
this appointment that changed the court
from six Republican-appointed justices
and three Democrat-appointed justices
to seven Republican-appointed justices
and two Democrat-appointed justices
(and though three more Republicanappointed justices retired before 1990,
all were replaced by other Republicanappointed justices). During this period,
the average vote margin each term fluctuated between 4.71 and 5.76 votes, all
very close to the expected margin of five
– a phenomena that suggests there is a
decent amount of conformity between
justices appointed by the same political party. In 1991, Justice Thurgood
Part II: Expected Margins vs. Actual
Margins
I
t is well-known that when vacancies
occur on the Supreme Court, presidents seek to fill those vacancies
with justices who share their political
12
Figure 2
Marshall (a Democratic appointee) was
replaced by Justice Clarence Thomas
(a Republican appointee). Yet though
the average vote margin increased following this appointment, it remained
at around six votes – somewhat below
the new seven-vote margin that would
have been expected following this Republican-appointed addition. In recent
years, following the appointments of
Sonia Sotomayor in 2009 and Elena Kagan in 2010, the Court’s expected vote
margin has dropped to one; interestingly, however, the actual vote margins
have mostly remained between five and
six votes. Nonetheless, this peculiarity
may be the result of new justices recusing themselves from certain cases in
their first years (Kagan, for example, abstained from ruling on cases that she had
previously encounte