Have the Political Parties Changed That Much?
There's a discussion of the claim that the major parties have switched positions over the past century at Statistical Modeling, Causal Inference, and Social Science (seen via God Plays Dice). I don't see how there has been that much of a change.
As fas as I can tell, the Republicans, from the start and continuing to the present, have been based on the following two principles:
Big business is America's persecuted minority and deserves an affirmative action program. (The first makes some sense, but I think the second part is going too far.)
Single-issue voters should always be taken seriously if they don't interfere too much with big business. This applied to anti-slavery voters, anti-alcohol voters, anti-abortion voters, etc. Sometimes this makes sense and sometimes it doesn't.
On the other side, the Democrats have always been about identity politics. They started out as the rural white identity-politics party and have gone through several changes in their list of favored ethnic groups since then.