Guts involves taking on Republican (8)
I believe the answer is:
entrails
'guts' is the definition.
(I've seen this before)
'involves taking on republican' is the wordplay.
'involves' becomes 'entails' (I've seen this before).
'taking on' is an insertion indicator.
'republican' becomes 'R' (abbreviation).
'entails' placed around 'r' is 'ENTRAILS'.
(Other definitions for entrails that I've seen before include "Internal organs of animals" , "Innards, viscera" , "Bowels or intestines" , "Intestines of animals" , "Intestines found in latrines" .)