Blunder by Republican boss (6)
I believe the answer is:
gaffer
'boss' is the definition.
('gaffer' can be a synonym of 'boss')
'blunder by republican' is the wordplay.
'blunder' becomes 'gaffe' (gaffe is a kind of blunder).
'by republican' becomes 'r' (abbreviation. I am not sure about the 'by' bit.**).
'gaffe'+'r'='GAFFER'
Can you help me to learn more?
(Other definitions for gaffer that I've seen before include "Informally, a boss or foreman" , "Chief electrician on a film set" , "Supervisor; chief electrician" , "man in charge" , "one securing large fish" .)