Lost in the GOP's euphoria over its landslide midterm victory is the fact that the Republican Party has almost become a whites-only party. Its strategy may win seats now, but it will lose over the long run.

Republicans won big in 2010 primarily because they won big among white voters. The 60% of the white vote that Republicans garnered last Tuesday is, by most estimates, the highest proportion of the white vote that the GOP has won in any national election since World War II.

Relying...