In the 1960s, both parties were in flux. The Democrats had traditionally been the racist party, while the Republicans had been far supportive of civil rights. But then both parties made a fateful choice. The Democratic Party – and its base – decided to support and fight for civil rights. It also made a lasting, long-term commitment to equality, and has actively embraced and promoted diversity for the past 40 years.
The Republican Party – institutionally, that is – went a different way. They adopted the Southern Strategy. They demagogued welfare queens. More generally, the party was institutionally hostile to laws and regulations and practices intended to correct centuries of state-sanctioned discrimination. To people like John Roberts, the world apparently began anew in 1964.
For years, the Republicans benefited from this choice. Nixon won. Reagan won. The South shifted to the GOP, giving it nearly 12 years of Congressonal control. Times were good.
But the checks are now coming due. The Democrats are beginning to see the benefits of the choices they made in the 1960s – the choices they remained firmly committed to over the years. Demographically, the country is getting less white. Individually, the most promising young African-American candidates and officials (people like Obama, Artur Davis, and Deval Patrick) are all firmly within the Democratic Party. Indeed, an entire generation of African-Americans have come of political age knowing nothing but hostility from Republicans and loyalty from Democrats.
He's basically right on the history. A commenter complains that Publius ignores the Democrats' showdown with the Dixiecrats in '48. This is true, but that showdown kind of went nowhere. The southerners decided to stay with the party through the 50s, resulting in softened stances on civil rights from Democratic leaders (including Adlai Stephenson(!) and Eleanor Roosevelt(!)), much to their shame.
It's convenient, but somewhat misleading, to think of the Democrats' abandonment of southern whites as a simple choice, as though they could have chosen to remain the party of Walter Mondale and Strom Thurmond into the 80s and 90s. Yes, some key choices were made --Kennedy (tepidly) integrating Old Miss, Johnson signing the Civil Rights Act, etc. But there were larger historical forces at work, as well. Outside the South, Democratic leaders had been pretty liberal since the New Deal, while Democratic leaders in the South were some of the most conservative politicians in the country. The only glue keeping those folks together was southerners' hatred of Lincoln. They got a lot of mileage out of that one, but it couldn't last forever.
I'm still partial to Polsby's air conditioning theory as an explanation of southerners' ultimate acceptance of Republicanism.