2012 California Senate - Emken vs. Feinstein

From the Civil War until the 1950s, California was solidly Republican.  But the Republicans who were elected were not Republicans in the modern sense of the word. Instead, like many party members in the West at the time, they hewed to a Progressive line. After the 1950s, Progressive Republicans in the northern portion of the state became Democrats, while conservative Democrats and suburbanites were switching and making the southern reaches of the state more Republican.

Today, California's political divide is more of an east-west split than a north-south one. Democrats represent the coastal areas, while Republicans dominate inland. Overall, the state has become solidly Democratic, in large measure due to the transformation of the suburbs into swing areas during the Bill Clinton years.

The prime beneficiaries of this were California's two Democratic senators, who came to Washington with Clinton.  Both survived narrow elections in the 1990s, but win handily today. Diane Feinstein's opponent this year is businesswoman Elizabeth Emken.