Revolutionary member of political party mostly offering nonsense (3)
I believe the answer is:
rot
'nonsense' is the definition.
(thesaurus)
'revolutionary member of political party mostly' is the wordplay.
'revolutionary member of political party' becomes 'trot' (abbreviation of Trotskyite).
'mostly' means to remove the first letter.
'trot' with its initial letter taken away is 'ROT'.
'offering' is the link.
(Other definitions for rot that I've seen before include "Gradual decline" , "Collapse" , "Decomposition" , "Break down, waste away" , "crumble" .)