U.S. vs staff member

U.S. and staff member both are nouns.

Word	Noun	Adjective	Verb	Adverb
U.S.	Yes	No	No	No
staff member	Yes	No	No	No

U.S. (noun)	staff member (noun)
the executive and legislative and judicial branches of the federal government of the United States	an employee who is a member of a staff of workers (especially a member of the staff that works for the President of the United States)
North American republic containing 50 states - 48 conterminous states in North America plus Alaska in northwest North America and the Hawaiian Islands in the Pacific Ocean; achieved independence in 1776