Clarification (at least from a USA perspective): Interviewers are not generally banned from asking about your political affiliation. In many states, there are protections against discrimination based upon political leanings, but they are not implemented across the board nationally.*
As a good rule of thumb: if you really want the job, do not volunteer potential employers anything about yourself that you don't think would help you get hired. They aren't cops or courts; depending on how laws are crafted state-to-state, they are legally allowed to consider some categories of information that they aren't legally allowed to ask you outright if you volunteer it.
*There are protections in place for the bureaucracy itself, but they were implemented for practical reasons early in the country's history when it was observed that a party change leading to a clean sweep of the federal government right down to the last front-desk agent regardless of their capabilities in the task at hand was highly inefficient.