Queen perhaps behind protest involving Republican politician (8)
I believe the answer is:
democrat
'politician' is the definition.
(I know that Democrat is a type of politician)
'queen perhaps behind protest involving republican' is the wordplay.
'queen perhaps' becomes 'cat' (a female cat is a queen).
'behind' means one lot of letters go next to another.
'protest' becomes 'demo' (demonstration).
'involving' means one lot of letters goes inside another.
'republican' becomes 'R' (abbreviation in US politics).
'cat' put after 'demo' is 'democat'.
'democat' placed around 'r' is 'DEMOCRAT'.
(Other definitions for democrat that I've seen before include "Believer in popular government" , "Advocate of government by elected representatives" , "Person who believes in government by and for the people" , "Cleveland?" , "Republican's US rival" .)