Brazen Republican divides party (5)
I believe the answer is:
brash
'brazen' is the definition.
(I've seen this before)
'republican divides party' is the wordplay.
'republican' becomes 'R' (abbreviation in US politics).
'divides' is an insertion indicator (inserted letters create a division or opening).
'party' becomes 'bash' (term for a party or celebration).
'r' going within 'bash' is 'BRASH'.
(Other definitions for brash that I've seen before include "Foolhardy" , "forward" , "Cocky and tactless" , "Offensively loud" , "Loud, garish" .)