Ill-fated party mounting protest (6)
I believe the answer is:
doomed
'ill-fated' is the definition.
(thesaurus)
'party mounting protest' is the wordplay.
'party' becomes 'do' (do is a kind of party).
'mounting' says the letters should be written in reverse (going up in a down clue).
'protest' becomes 'demo' (I've seen this before).
'demo' in reverse letter order is 'omed'.
'do'+'omed'='DOOMED'
(Other definitions for doomed that I've seen before include "Fated" , "Under sentence" , "Ill-fated" , "Condemned to destruction" , "Condemned to certain death" .)