Barack Obama's decisive victory reaffirms a pattern that dates back to the dawn of the Republic. Every 30 years or so, a new popular movement challenges established party identification and precipitates a reorganization of the electorate. From Jefferson to Jackson, Jackson to Lincoln, Lincoln to William Jennings Bryan, Bryan to Franklin D. Roosevelt, and FDR to Martin Luther King Jr., this cycle of change plays out with remarkable regularity. Twenty-eight years after the most recent pivotal election -- Ronald Reagan's victory in 1980 -- Obama has arrived right on schedule. The cycle is propelled by the rising generation's changing views on fundamental questions -- the role of government in the economy, the place of equality in social life, the balance between security and liberty. Voters form views in response to a crisis and hold fast until the next shock comes along. The Reagan revolution responded to the malaise of the 1970s. Long gas lines, inflation, judicial activism, and the...