It's hardly a mystery. It's human nature to form ourselves into groups and exclude those who are different. Liberals possess this characteristic to an unusual degree. Once they reach a critical mass in any field, be it the news media or acadamia, they automatically move to banish all who are different from themselves, and put up barriers to keep those "others" out. I've even seen this at play in more ordinary fields, such as IT companies. A liberal in a position of power will fire a conservative programmer without batting an eye.

One basic question, for both social-science behaviorists and political philosophers, is: what explains the subjects' prior orientation Democrat or Republican?

Is it the result of a decision? If so, then how would the political-bias mental operation work, exactly? It would seem that even behaviorists would ultimately have to answer that question -- even (or especially) if they factor in variables like family upbringing, religious affliation, race, socioeconomic status, or anything other than a meteor strike. A kind of reductio ad rationem, then.

But then again, in politics accident and force usually trump reflection and choice. Go figure.

So they cannot help themselves? Isn't there supposed to be something unstable about compulsive behavior?

Hey, it's science. Any Glowball Warmening believer can tell you that you have to go with the science.