Irritable Democrat, typically somewhat diminished (5)
I believe the answer is:
ratty
'irritable' is the definition.
(I've seen this before)
'democrat typically somewhat diminished' is the wordplay.
'diminished' indicates the answer is hidden within the clue (a smaller amount of the letters).
'RATTY' is hidden within 'democrat typically somewhat'.
(Other definitions for ratty that I've seen before include "Irritable, peevish" , "Character created by Kenneth Grahame" , "Bad-tempered, irritable as a rodent" , "with pests" , "character on the river bank" .)