How Do Mainstream Parties React to the Rise of Extremist Parties?

By Indridi Indridason, Professor at the University of California, Riverside

What is the story?

In many European countries, the last decades have been marked by the rise of extremist parties such as the FN in France, the UKIP in the United Kingdom, or the PVV in the Netherlands. Extremist parties are often seen as threats to democratic systems because of their illiberal values. Yet extremist parties rarely enter government and, therefore, have limited influence on policy. However, the popular perception is that mainstream parties sometimes co-opt some of the issues extremist parties advocate, such as greater restrictions on immigration. A problem with this perception is that it based on countries where extremist views enjoy a sizable support. The counterfactual, that is, how mainstream parties would behave if there was no extremist party, is not considered. In this article, I present a theoretical model of electoral competition in the presence and in the absence of an extremist party under both first past the post (FPTP) and majority run-off electoral rules and derives predictions about the final policy implemented by the government.

A model of electoral competition under FPTP

I consider a simple spatial model in which two mainstream political parties compete with an extreme party under a FPTP system. The mainstream parties are assumed to choose their policy platforms strategically so that the policy implemented by the government is as close as possible to their ideological position. In contrast, the extremist party is assumed to be ‘expressive’, that is it simply campaigns on its most preferred policy position and does not adapt its platform. For the sake of convenience, the extremist party is here assumed to be far-right.

The counterfactual considered in this model is the policy implemented by the government when the extremist party does not compete. This equilibrium is well-known: Both parties adopt the platform that corresponds to the median voter’s preferred policy. In other words, both mainstream parties tend to move to the centre of the ideological spectrum. As a consequence, the policy eventually implemented by the winner, no matter which party wins, is centrist.

However, when an extremist party presents a candidate, it is shown that there is an equilibrium where (1) the winner of the election is always one of the mainstream parties and (2) the policy platform of the winning party is more left-leaning than what it would have been without an extremist party. In other words, in the presence of an extremist right party, mainstream parties tend to move to the left on the ideological spectrum. One way to make sense of this result is to think about the far-right voters. These voters always support the extremist party. As mainstream parties have no chance to capture them, they will concentrate on left-wing voters. From the perspective of the mainstream parties, the presence of a right extremist party truncates the distribution of voters on the right. Their median voter of the mainstream voters is further to the left than the median voter of all the voters. Figure 1 offers a graphical representation of this idea. Assuming that voters are normally distributed along the left-right spectrum, the median voter in the situation where there is no extremist party (above) is more right-wing than in the situation where there is a one (below). The shaded area represents the fringe of voters that vote for the extreme party.

The model of electoral competition under majority run-off

Formal theorists have long been aware of this incentive for mainstream parties to move away from an extremist’s policy position under FPTP. However, this incentive has not been characterized in the context of majority run-off elections. In majority run-off elections, mainstream parties also move away from the extremist party but they do so to a smaller extent. One concern of the mainstream parties is to prevent the extremist from qualifying for the second round, which means that sometimes one of the mainstream parties has to `sacrifice’ its chance of winning by adopting a policy platform closer to the extremist party in order to deprive it of votes. This party thus adopts a platform closer to the extremist party. In effect, this gives the appearance of the party co-opting the policies of the extremist party whereas the government policy is at the end further away from the extremist party.


Contrary to what many people think, the presence of an extremist right-wing party does not attract mainstream parties to the right-wing of the ideological spectrum. To the contrary, in these situations, mainstream parties tend to adopt more left-leaning policy platforms. While this prediction is valid under both FPTP and majority run-off electoral systems, the move to the left is more marked under the former.

In the end, we are left with what an interesting puzzle: If the decision of the extremist parties to compete makes the policy of the government more left-wing, why do they decide to compete? In my model I simply assume that extremist parties are ‘expressive’ and that they just want to show their policy position. Whether that is a plausible assumption is open to debate. What my results demonstrate is that if extremist parties do manage to shape the political agenda, it happens through some mechanism other than electoral competition.

For a more precise description of the model and further implications, see Indridason, Indridi. 2013. Expressive Motives & Third-Party Candidates. Journal of Theoretical Politics, 25: 182-213.

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