VoxEU Column Politics and economics

The impact of US immigration on Democratic and Republican election outcomes

Immigration is an important election issue that often benefits right-wing political parties. Contemporary European politics is an example par excellence. Immigration in the US has been intermittently at the fringes and centre-stage in recent years, and this column looks at the extent to which US voters care about immigration. The political effect of immigration turns out to crucially depend on the extent to which immigrants participate in the political process. One thing from the research is clear: Republicans are generally opposed to immigration reforms, especially if they include a path to citizenship for currently undocumented immigrants. Naturalised immigrants are a liability for conservative politicians, as they tend to vote for progressive parties.

The refugee crisis in Europe and the debates among the primary election candidates in the US have brought immigration-related issues to the front pages of newspapers in the last months.  Political leaders all over the world cannot ignore the impact that immigration has on voters and often they use it to their political advantage. The aggressive stance of Republican candidates towards undocumented immigrants in the US and the belligerent positions of right-wing candidates against refugees in Europe have become common features of the news. Immigration may have a defining effect on political outcomes (e.g. Ortega 2005) and politicians are certainly aware of that. Yet, only recently has the empirical literature in economics and in political science started to look systematically at the connection between immigration and the electoral success of different political parties.

The existing studies in the literature have focused on individual countries, mainly in Europe, and they provide evidence consistent with the idea that right-wing parties stand to gain votes from more immigrants. Three recent papers (Barone et al. 2014, Halla et al. 2012, and Otto and Steinhardt 2014, focusing respectively on Austria, Italy, and on the city of Hamburg, Germany) found that recent immigration was correlated with the increased political success, measured by shares of votes, of the extreme right-wing parties. The anti-immigration stance of those parties, it appears, has become more appealing to citizens as new immigrants have grown to be a larger local presence. But does this rhetoric work in the US?  Are voters in a country built on successive generations of immigrants driven to vote Republican because of increasing immigration pressure?

In a recent paper on immigrants and election outcomes in the US (Mayda et al. 2015) we show that, on average, immigration in a US state decreases the electoral success of the Republican party,1 especially in the House elections.

Figure 1. Correlation: Republican vote share vs. immigration share

Figure 1 plots the simple correlation between the change in the share of Republican votes between 1994 and 2012 and the change in total immigrants as a fraction of the adult population during the same period across US states. The visual impression is clear and confirmed by the statistical significance of the regression coefficient – there is a negative and high correlation between the growth in the immigrant share of the population and the Republican vote. In states that experienced an increase of immigrants by 1% of the population, the Republican Party received 1% fewer votes.

Citizen and non-citizen immigrants

One crucial element to understand the effect of immigrants is to decompose their impact on votes in two channels, each of them captured by a specific group of immigrants.

  • The first channel captures the indirect political effect of immigration working through the impact on existing voters who are mainly natives.

The social and economic impact of immigrants, as perceived by citizens, affects how they cast their vote – and this perceived effect is stronger the more numerous immigrants are.

  • The second channel is related to the direct political role of immigrants as voters.

As they become naturalised, immigrants affect elections to the extent that they vote differently from natives. Immigration, therefore, may have different impacts depending on the balance of immigrant citizens and non-citizens and on how strong the voting response of citizens is to their presence.

In the US, the media and political analysts have focused mainly on the direct effect, pointing out the potential adverse impact that migrants can have on the electoral success of the Republican Party, as immigrants seem more likely to vote for the Democratic Party. Some political commentators even see an inevitable demise of the GOP in the long-run, as first-generation immigrants become more numerous and vote for the Democrats. In our paper, we confirm this prediction by showing that, on average, immigration to the US has a significant and negative impact on the Republican vote share.

An important aspect of the political effect of migration, which has received less attention in the US debate, is that natives' votes too can be affected by the increase in the share of immigrants, through the indirect channel described above. When we distinguish between the effect of naturalised and non-naturalised immigrants, our empirical analysis shows that this is indeed the case. The impact of immigration on Republican votes in the House is negative when the share of naturalised migrants in the voting population increases. Yet, it is positive when the share of non-citizen migrants increases above a threshold.2 Our results are consistent with naturalised migrants being less likely to vote for the Republican Party than native voters, and with native voters' political preferences moving in favour of the Republican Party but only at high levels of non-citizen immigrant shares. This second effect is significant only for quite high shares of (non-citizen) immigrants (above 0.132). According to CPS data as of 2012, only in six US states (California, District of Columbia, Nevada, New Jersey, New York and Texas) was this share sufficiently high to push natives towards the Republican Party. For the other states, the share of non-naturalised immigrants in the population was less than 13.2% in 2012 (and it still is) and the corresponding impact on Republican votes of non-citizen immigrants was null to negative.3

Reconciling the evidence from Europe

The differential impact of citizen and non-citizen migrants can be at the core of the contrasting empirical evidence coming from Europe and the US.

  • According to our results, the political effect of immigration crucially depends on the extent to which immigrants participate in the political process.

To the extent that naturalisation rates and/or political participation of immigrants are low in Europe, the indirect political effect, working through the impact on existing voters, dominates. This effect exists in the US too, but it appears to be weaker and only positive for the Republican vote share at very high shares of non-naturalised citizens. Overall, on average, the direct effect of immigrants dominates.4 When we differentiate across states/years cells, according to their share of non-naturalised migrants, we find that only six states have a high enough share of non-naturalized immigrants to generate a positive effect on Republican vote shares.

Implications for the political landscape in the US

Looking at the debate surrounding immigration policy reform in the US, one message is clear. For the most part, Republicans are opposed to reforms, especially if they include a path to citizenship for currently undocumented immigrants. In addition, in electoral times, Republicans’ average attitude towards migrants is to talk ‘tough’ about the presence of undocumented immigrants. Our results shed light on both these issues.

  • First, naturalised immigrants are a liability for conservative politicians, as they tend to vote for progressive parties.

Hence the incentive for Republicans to turn 11 million undocumented immigrants into voters for the Democratic Party is low.

  • Second, the presence of undocumented immigrants is the raison d'être of some conservative politicians.

Right-wing parties in Europe and vocal anti-immigration Republicans in the US flourish in localities and times characterised by a high non-citizen immigrant share. In the US, Republicans gain votes when the high local share of undocumented migrants makes American voters more conservative.

The political returns of making undocumented immigration a salient issue, however, may be limited. According to our calculations the non-citizen immigrant share is high enough to help Republican votes only in a handful of states.


Baerg, N, J L Hotchkiss, and M Quispe-Agnoli (2014), “Unauthorized Immigration and Electoral Outcomes”, Andrew Young School of Policy Studies Research Paper Series.

Barone, G, G De Blasio, and P Naticchioni (2014), “Mr. Rossi, Mr. Hu and Politics: The Role of Immigration in Shaping Natives’ Political Preferences”, IZA Discussion Paper 8228.

Halla, M, A F Wagner, and J Zweimuller (2012), “Does Immigration into Their Neighborhoods Incline Voters Toward the Extreme Right? The Case of the Freedom Party of Austria”, IZA Discussion Paper 6575.

Mayda, A M, G Peri and W Steingress (2015), “Immigration to the US: A problem for the Republicans or the Democrats?” CEPR Discussion paper 11001, IZA Discussion Paper 9543.

Ortega, F (2005), “Immigration quotas and skill upgrading,” Journal of Public Economics 89: 1841-1863.

Otto, A H and M F Steinhardt (2014), “Immigration and election outcomes: Evidence from city districts in Hamburg”, Regional Science and Urban Economics 45: 67-79.

Reichel, D (2012), “Regulating Political Incorporation of Immigrants – Naturalisation Rates in Europe”, ICMPD Working Paper 4.


1 This analysis is based on variation across US states and years between 1994 and 2012 – using data from the Current Population Survey merged with election data.

2 This is consistent with Baerg et al (2014), who estimate a negative impact of unauthorised workers on votes to the Democrats in the US state of Georgia, using variation across counties.

3 At the Congressional-district level, using estimates of the non-citizen migrant share based on the American Community Survey for the 114th Congress, we find that only 55 out of 434 Congressional districts have large enough non-citizen shares to produce a positive impact on the Republican vote.

4 According to the American Community Survey, in 2008 the US naturalisation rate was 43%. In many European countries naturalization rates were lower in the same year, for example in Italy (14%) and in Austria (34%) (Reichel 2012).

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