Party returning weak Tory leader (5)
I believe the answer is:
troop
'party' is the definition.
(thesaurus)
'returning weak tory leader' is the wordplay.
'returning' is a reversal indicator.
'weak' becomes 'poor'.
'tory leader' becomes 't' (I've seen this in other clues).
'poor'+'t'='poort'
'poort' reversed gives 'TROOP'.
(Other definitions for troop that I've seen before include "Military unit" , "Military body" , "March" , "Flock, crowd" , "herd" .)