Supreme Court (SCOTUS)
The US is 9 seats. It is US-only. Holding a justice seat does not occupy your current office: you can sit on the Court and still be a Senator, governor, or private citizen.
Seats
Each seat has a current occupant (a player, an , or a scripted historical justice) or is vacant.
Until a seat's first live confirmation, it replays an Original Roster: historical occupants succeed each other on authored years with no vacancy gap. The first presidential nomination that confirms a new justice is the divergence point for that seat. After that, succession is in-game.
Nomination and confirmation
The President nominates. The Senate confirms by simple majority, using the same seat-weighted Senate vote machinery as cabinet confirmation. See Confirmation Process.
A justice seat is not a cabinet office and is not gated by year the way HUD or Homeland Security are.
Docket
Curated historical cases resolve against the sitting Court. A majority on the case's tagged axis can diverge from the historical outcome; a divergence can enact policy through the same bill-enactment pipeline as legislation.
Surprise cases can also fire: non-historical docket items that resolve the same turn they spawn. They still produce a ruling from the sitting majority.
Tenure
Scripted historical occupants leave when their authored departure is reached. After divergence, a sitting justice (player or NPP) can leave mid-term; the President and occupant are notified when a seat opens. The Court does not keep a confirmed player forever.
See also: Bills & Legislation, Cabinet, Impeachment.