How much choice does an admiral have over staff?

How much input does an admiral have into choosing a command staff?

Historically, an admiral had much wider choice; modern commanders are usually offered a limited selection, though they can often bring trusted staff with them.

Admirals once had broad latitude to select any available officer for their staff. Modern appointments offer a more limited list of candidates, although commanders can usually bring officers from a previous staff. Individual officers also have some ability to decline a position when they have a reason. Refusal can harm their careers, so that choice carries a cost.