We exploit plausibly exogenous variation in European immigration to US cities between 1910 and 1930 induced by World War I and the US Immigration Acts to study if the inflow of immigrants triggered natives’ backlash. Using local newspapers data, we document that immigration fueled anti-immigrant sentiments and increased the frequency of racially charged words against the foreign born (e.g. “Inferior Races”; “Beaten Races”; etc.). Racist reactions were entirely driven by Catholic and Jewish (but not by Protestant) immigration, suggesting that natives’ backlash had cultural, rather than economic, foundations. Consistent with this interpretation, we do not find any evidence of heterogeneity in newspapers’ rhetoric depending on city economic characteristics. Our findings further indicate that European immigration generated “contagious animosity” towards other minority groups - in particular African Americans and Chinese immigrants already living in US cities. Finally, we complement our analysis by using Congressional speeches from the Senate, and applying supervised machine learning methods. In line with newspapers’ reactions, Senators representing states that received more immigrants during the previous decade were significantly more likely to adopt a racist rhetoric when discussing immigration-related bills. One possible interpretation of our findings – though not the only one – is that politicians responded to changes in demands from their constituencies, and switched to a racist rhetoric following their voters’ sentiments.