So many questions. How are users tagged D or R? Is that a manual process or automated somehow? What is the effect of these tags? Can I find out if my Twitter account is in one of those buckets?
you could probably algorithmically determine it in most cases based on any number of indicators from phrases used, to communities interacted with, which hashtages are included, which cohort retweets and likes most etc... thats not even getting into simply tagging political figures with the party they officially affiliate themselves with
Likely they are tracking performance verified politician accounts based on registered party affiliation. Why republican should count equal in the evaluation metric to democrat when nunerically there are less republican voters, let alone proportions on Twitter, is another question.
And how are they choosing to balance them, per capita, or just both sides should get 50%? It seems pretty clear they are making editorial decisions here. Does that break their section 230 protections?