Have you ever been a member of or in any way associated (either directly or indirectly) with a Communist Party?
I grew up in Vietnam, came to US when I was 16. Vietnam is a communist country but I never joined/worked for the government? Should I answer no or yes because of the word "indirectly"?
I grew up in the Soviet Union and there it was essentially mandatory for children at 14 years of age to join KOMSOMOL, which was the USSR Communist Youth League, an affiliate of the Communist party of the USSR. The membership in KOMSOMOL was from 14 y.o. to 27 y.o., and almost everybody in that age group was a member. E.g. during the Soviet period it was impossible to get into college without being a KOMSOMOL member, and an expulsion from KOMSOMOL meant mandatory expulsion from the university/college.
I was a member as was everyone else whom I know in my age group. So most people who grew up in the Soviet Union and who were members of KOMSOMOL answer "yes" to this question in N-400. I answered "yes" and attached an explanation. It was not a problem during the interview and the IO did not ask any questions about this point. I have not heard of anyone else who answered "yes" for the same reason experiencing any problems at the interview regarding this issue.
However, I
did hear stories about people who answered "No" (despite of being KOMSOMOL members when in high school and college) and then did run into trouble at the interview. Most IOs are perfectly well aware that essentially everybody who grew up in the Soviet Union was a member of KOMSOMOL and they expect such applicants to answer "yes". Lying in this situation and being caught lying is much more likely to land one in trouble than telling the truth.
Plus, as I remember, there was a similar question in I-485, and I remember answering "yes" to that one as well. At the very least, having answered "yes" in I-485, one should then be consistent and answer "yes" in N-400 as well.
I don't know for sure about Vietnam, but I suspect that Vietnam had (or maybe still has) an analog of KOMSOMOL.
If you were a member of it, then you probably should answer "yes".