What are the effects of entry of new extremist parties on the policy platforms of mainstream parties?
| Date | 01 July 2019 |
| DOI | 10.1177/0951629819854138 |
| Author | Samuel Merrill,Bernard Grofman |
| Published date | 01 July 2019 |
| Subject Matter | Articles |
Article
Journal of Theoretical Politics
2019, Vol.31(3) 453–473
ÓThe Author(s) 2019
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DOI: 10.1177/0951629819854138
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What are the effects of entry
of new extremist parties on
the policy platforms of
mainstream parties?
Samuel Merrill
Professor Emeritus, Departmentof Mathematics and Computer Science, Wilkes
University,USA
Bernard Grofman
Department of Political Science and Center for the Study of Democracy, University of
California-Irvine, USA
Abstract
We examine the consequences to policy-seeking, center-left and center-right parties under pro-
portional representation following entry by extremist partieseither at one or both ends of a unidi-
mensional political spectrum. Assuming a symmetric, unimodal voter distribution, we show that
the entry of a single extremist party on either the left or right drives both mainstream parties in
the direction opposite to the extremist party. Weargue that this three-party scenario is the most
empirically relevant case incontemporary European politics. We also extendresults of Casamatta
and De Donder that project moderation of mainstream parties at equilibrium for PR elections
with two extremist parties – one on each end – to a symmetric, unimodal voter distribution. In a
setting not considered by these authors, we show that this moderating effect on the mainstream
parties for a symmetric voter distribution is reversed if the voter distribution is sufficiently
bimodal.
Keywords
Extremist parties; Mainstream parties; Party competition; Policy-seeking; Voter distribution
Corresponding author:
Samuel Merrill, III, ProfessorEmeritus, Department of Mathematics and Computer Science, Wilkes University,
3024 43
rd
Ct. NW,Olympia, WA 98502, USA.
Email: smerrill@mathcs.wilkes.edu
I. Introduction
Adams and Merrill (2006) trace the consequences of the entry into unidimensional
political competition by a centrist party in a two-party situation with single-seat
competition under plurality where there is a center-right party and a center-left
party, both of which are policy-seeking, i.e., entry that changes a two-party game
into a three-party game. While Duvergerian ideas of the dynamics of plurality-
based competition (see Duverger, 1954; Fey, 1997; Palfrey, 1984) might suggest
that the center-right and the center-left party would operate to squeeze out the cen-
ter party by each moving further to the center, Adams and Merrill demonstrate the
counterintuitive result that, if the major parties are both policy-seeking parties,
they can be expected to propose policies that are much more divergent than what
we should observe without the third party.
While new parties of many stripes may enter the political process, a common
phenomenon today, especially in European polities, is the appearance of an
extreme party that substantially cuts into the support of more centrist parties.
Most commonly this extremist party is a populist party on the right (see Abou-
Chadi and Krause, 2018; Eatwell, 2017; Kitschelt with McGann, 2017; Mudde,
2017; Widfeldt, 2014). We model this situation as a three-party game, with a
center-right and a center-left party initially, followed by the entry of an extremist
party – thus converting a two-party game into a three-party game. Such a scenario
can be thought of as a natural complement to the Adams-Merrill (2006) set-up.
We first highlight the consequences of the entry of a single extremist party at
one end of the political spectrum, since we believe this scenario has considerable
empirical relevance, not just in proportional representation (PR) settings, which
are the focus of this paper, like the Netherlands, but also in plurality settings, such
as the UK, and in two-round elections, such as in France. But sometimes we have
extremist parties entering the political space from both ends of the political spec-
trum – although usually in recent decades it is the right-wing party that is the
greatest threat to the center. This possibility leads us to consider the four-party
case, with a center-right and a center-left party at the beginning followed by entry
of more extreme parties from both sides of the political spectrum. When there are
two new extremist parties, one at each end of the spectrum, we extend findings of
Casamatta and De Donder (2005) from log-concave voter ideal densities to any
symmetric unimodal densities. Then we provide a new theorem that extends their
work further, by examining what happens when the underlying voter distribution
is bimodal.
We see our modeling as very relevant to events in the real world in terms of the
decline in the vote share of mainstream parties throughout much of Europe (includ-
ing the UK) and the response of established parties to new and more extreme ones
that begin to garner substantial voter support. Our set-up allows us to consider
both the empirically common case where it is a new (or renewed) right-wing party
that is the greatest threat, and the case where the threat to the center comes from
both ends of the spectrum.
454 Journal of Theoretical Politics 31(3)
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