The conclusion is inescapable and uncomplicated. As the immigrant population has grown, Republican electoral prospects have dimmed, even after controlling for alternative explanations of GOP performance. A typical drop in Republican support in a large metro area county is about six percentage points. In other words, an urban county that cast 49 percent of its vote for the Republican candidate in 1980 could be expected to drop to 43 percent by 2008.
Across all U.S. counties, including many rural counties, the estimated effect of immigration is to drop Republican vote share 1.7 to two percentage points. Even in seemingly remote locations with negligible immigrant populations, the effect is sufficient to move a 51 percent county to a 49 percent county. Aggregated over the large number of counties and viewed through the template of the Electoral College’s winner-take-all system of elections, the impact of immigration is easily sufficient, by itself, to decide many current and future presidential elections.
An opposition party can hold together and rally the public against an unpopular opponent, but once it takes power, internal fissures grow more prominent and a skeptical public becomes much less indulgent. The ongoing trends mentioned above will make the task of governing even tougher for the Republicans, should they regain power, than it now is for the Democrats.
This long-term lesson must not be lost on the GOP. Relying on Obama and the Democrats to double-fault may win one election, but is unlikely to produce a lasting majority. If the Republicans do not resolve their internal tensions and adjust to demographic shifts and changing public attitudes, they could easily resume their decline and perhaps even go the way of the Whigs.