Caucus is also one of two ways state branches of political parties can nominate a person to be a candidate for election (the other being a primary).

The author likely lives in a state where such a thing happens (both parties use primaries where I live, but the term is not unfamiliar at all).

https://th.usembassy.gov/primaries-caucuses-differences/

You might want to tone down the hyperbolic aggression. It isn't the author's fault for using a word in a fitting analogy just because you're not familiar with it.

This is the third article in a series, and the term is fairly clearly described in a previous article, linked at the top.

Missing that (and thus the question that started this thread) is okay. Your aggression is not.