Is it legal under current law to discriminate based on political affiliation?
I am not sure, but I think there is a strong correlation between sound thought, logic, sound reasoning and political affiliation. There is no reason to ask a person about their political affiliation. It is easy to determine indirectly though good interview questions and past employment history.
For instance, I would never hire someone that worked for the National Organization for Women (NOW). I really don't care about their excuses or conservative conversion that they may have had. There is something fundamentally wrong with a candidate with that work history.