I must admit, the notion of being "in" a party in a way an employer can easily check, or party affiliation that is legally registered, is outside my experience.

I must admit, the notion of being "in" a party in a way an employer can easily check, or party affiliation that is legally registered, is outside my experience. By affiliation I meant only the party a person tells other people they support, in a non-binding social sense. I'm not in the USA. I agree, where affiliation with a party has greater meaning and consequences, and is practically required for access to ordinary local services, the secret ballot is even more important. That neighbourhood is a great example. I'm disappointed, really, that in 21st century USA those people are still disenfranchised by local politics from voting in the primary of the party they actually support. But presumably there are good reasons for legal registration.