Party favourite in power (8)
I believe the answer is:
dominion
'power' is the definition.
(thesaurus)
'party favourite' is the wordplay.
'party' becomes 'do' (do is a kind of party).
'favourite' becomes 'minion'.
'do'+'minion'='DOMINION'
'in' acts as a link.
(Other definitions for dominion that I've seen before include "Area of control" , "Authority to rule over and control people" , "Realm" , "Sovereignty, control" , "territory" .)