For anyone who is interested in some of the history to this.
There’s the famous “switch in time to save nine” (link to wiki below). I’m too lazy to refresh my memory, but the court was worried FDR was going to add justices to the bench to make sure his New Deal legislation (or whatever) would get passed. A sitting justice (or more) famously switched his political view on issue(s) to keep it from happening, and the number of justices was preserved at nine, which we have today.
https:// en.wikipedia.org/wiki/The_switch_in_time_that_saved_nine