||How is two-party electoral competition influenced by third parties, even under normal
political conditions? I argue that the mere threat of third party entry into the
election induces anticipatory electoral strategies by the major parties. This effect,
which is a normal aspect of the two-party system, is how third parties play a consistent
role in U.S. elections.
The ability for third parties to influence the major parties is moderated by electoral
institutions. The ballot access requirement, in the form of a signature requirement,
varies widely across House elections and is a significant predictor of third party
electoral success. Consistent with conventional wisdom, I find that it has a negative
effect on the likelihood of entry. Notably, the requirement also has a positive effect
on third party vote shares, conditional on successful petitioning, due to a screening
and quality effect.
I explore the effects of third party threat in unidimensional and multidimensional
settings. A formal model of elections predicts that the threat of entry induces major
party divergence in a unidimensional ideological space. The major parties diverge
in anticipation of potential third party entry. An empirical analysis of candidate
positioning in the 1996 U.S. House elections finds support of this hypothesis.
Data on major party campaign advertising in the 2000 to 2004 U.S. House elections
are used to assess third party effects in a multidimensional framework. I show that
third party threat influences the scope and content of campaign advertising. Major
party candidates, particularly incumbents, discuss a broader range of issues when
third party threat is higher. I use the case of environmental issues and the Green
party to assess the influence of third parties on issue-specific content. I find
that Green party threat leads to predictable differences between Democratic and Republican
advertising on environmental issues.
In sum, third parties play a consistent role in U.S. House elections by inducing anticipatory
strategies by the major parties. This strategic framework for understanding third
parties stresses two things. First, one should focus on the major parties in order
to gauge the influence of third parties. Second, one should not conclude that third
parties are irrelevant because of their minimal electoral success. Third party effects
are in fact present even in elections where a third party does not enter.