As I put in my earlier conversation with Eric:
Each party has no fixed position, but two definite constituencies:
- The people who will vote for the party’s candidates
- The people who will contribute money to the party
For the Republicans the ideology of the median contributor is fairly close to the ideology of the median voter. For the Democrats, the median contributor seems to be farther left than the median voter. This pushes the party ever leftwards (and indirectly pushes the Republican’s leftwards as well).
I suppose the question is: Is this an evolutionary stable strategy? Time will tell I suppose.