Denial of unhappiness with leader becoming Republican (9)
I believe the answer is:
rejection
'denial' is the definition.
(thesaurus)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for rejection that I've seen before include "Brush-off" , "Refusal - treatment as worthless" , "Refusal, renunciation" .)