I'm sure there are plenty of close friendships between ideologically very different justices or politicians and even when there isn't, they are still generally civil with their colleagues and mostly get along. The extreme polarization and ominous rhetoric about what will happen if the other side gets in power is to a large extent a political performance.

The linked article is a particularly whiplash-inducing example - from one paragraph to the next, Ted Cruz goes from praising RBG and discussing his experiences working with her, to producing absurd apocalyptic rhetoric about what would happen if a Democrat president is allowed to pick her replacement instead of Trump. It's completely ridiculous and he knows it, but in today's American politics, spouting such nonsense is what it takes to remain popular as a senator and drum up votes for the next election.