Political Extremism in the US: The Effects of Migrant Communities 

Abstract: Rising political extremism has been one of the defining trends of the past decade. Explanations for this phenomenon include increased globalization, rising inequality, slowing economic growth rates, the aftereffects of the Global Financial Crisis, and a backlash against increasing migrant flows. My study focuses on this last explanation, trying to explain the extent to which migration drives political extremism in the United States. While there is a literature examining this issue in Europe, this is the first to consider this within the context of the U.S. Using a new measure of political extremism derived from campaign contributions, I am able to measure political extremism of candidates themselves rather than the extremism of their political party. I am also able to observe extremist positions for both winning and losing candidates, an advantage over relying on voting behavior to measure extremism. 

I find that right-wing extremism in the U.S. is strongly affected by migration. A 1 standard deviation in the foreign-born population share of a Congressional district increases the likelihood of an extremist Republican candidate by about 11 percentage points. There is not a corresponding effect of migration on the proclivity of Democratic candidates to adopt extremist positions.  Despite migration driving right-wing extremism, candidates adopting extremist positions tend to have poor electoral results. The presence of an extremist Republican candidate in an election drives Republican vote shares down by 2.3 percentage points and Democratic vote shares up by 8.8 percentage points. The presence of an extremist Democratic candidate causes both Democratic and Republican candidates to lose just under 2 percentage points off their vote share. This suggests that extremist right wing positions benefit democratic candidates in general elections, while extremist left wing positions siphon voters away from both parties and toward third party candidates. 

The key takeaway from this study is that right-wing extremism is more likely to occur in areas with large foreign-born populations. This suggests that extremism may be a winning strategy in primaries where candidates are facing off against a larger number of opponents and extremist views may be more mainstream. However, extremism becomes a liability in general elections, with extremist candidates (and especially right-wing extremists) performing poorly in general elections.