Obama is about to roll out the welcome mat for immigrants once more; here's why

Although high immigration may work against Democratic policy goals, such as raising wages for the poor and protecting the environment, it does improve Democratic electoral prospects. In contrast, immigration may help Republican business interests hold down wages, but it also undermines the party’s political fortunes. Future levels of immigration are likely to be a key determinant of Republicans’ political prospects moving forward.

•The electoral impact of immigration has been greatest in counties with large populations, where most immigrants settle. In these locations, Republicans have lost 0.58 percentage points in presidential elections for every one percentage-point increase in the size of the local immigrant population. On average the immigrant share has increased 9.5 percent in these counties.

•In counties of at least 50,000, where the immigrant share increased by at least two percentage points from 1980 to 2008, 62 percent saw a decline in the Republican percentage. In counties with at least a four percentage-point increase, 74 percent saw a decline in the GOP vote. In counties with at least a six percentage-point gain in the immigrant share, 83 percent saw a decline in the GOP vote share.

•Republicans have remained competitive in presidential elections because losses in high-immigration counties have been offset by steady gains in low-immigration counties.

•Even in Texas and Florida, often thought to be an exception, the rising immigrant population across counties is associated with sharply diminished support for Republican candidates.

•In Texas, for example, the estimate shows that for every one percentage-point increase in the immigrant population in a county, the Republican vote share dropped by 0.67 percentage points, which is more than the decline nationally association with immigration.

•The decline does not seem to be associated with the local Republican Party’s position on illegal immigration.