Fatter Republican is into beer (6)
I believe the answer is:
larger
'fatter' is the definition.
Both the definition and answer are comparative adjectives. Perhaps you can see a link between them that I don't see?
'republican is into beer' is the wordplay.
'republican' becomes 'r' (abbreviation).
'is into' is an insertion indicator.
'beer' becomes 'lager' (type of beer).
'r' inserted within 'lager' is 'LARGER'.
Can you help me to learn more?
(Other definitions for larger that I've seen before include "more stout" , "Ebullient person may be describes as ?? than life" , "Comparatively bigger" , "Bigger, greater" , "Comparatively big" .)