From the summary:
This Backgrounder examines the partisan political implications of large-scale immigration. A comparison of voting patterns in presidential elections across counties over the last three decades shows that mass immigration has caused a steady drop in presidential Republican vote shares, particularly in the nation’s largest counties. Each one percentage-point increase in the immigrant share of a large county’s population reduces the Republican share of the two-party vote by nearly 0.6 percentage points on average.
Three key conclusions emerge from this analysis:
– First, the enormous flow of legal immigrants in to the country — 29.5 million 1980 to 2012 — has remade and continues to remake the nation’s electorate in favor of the Democratic Party.
– Second, the partisan impact of immigration is relatively uniform throughout the country— from California to Texas to Florida — even though local Republican parties have taken different positions on illegal immigration. The decline does not seem to vary with the local Republican Party’s position on illegal immigration.
– Third, if legal immigration levels remain at the current levels of over one million a year, it will likely continue to undermine Republicans’ political prospects moving forward. Further, if the substantial increases in legal immigration in Senate’s Gang of Eight bill (S.744) were to become law it would accelerate this process. Conversely, lowering the level of legal immigration in the future would help stem the decline in the Republican vote….