US state is joining right-wingers in victory (9)
I believe the answer is:
wisconsin
'us state' is the definition.
(I've seen this before)
'is joining right-wingers in victory' is the wordplay.
'joining' says to put letters next to each other.
'right-wingers' becomes 'cons' (abbreviation for conservatives).
'in' is an insertion indicator.
'victory' becomes 'win' (a win is a victory).
'is'+'cons'='iscons'
'iscons' going into 'win' is 'WISCONSIN'.
(Other definitions for wisconsin that I've seen before include "Northern state" , "US state, capital Madison" , "State of N. central US" , "The "Badger State"" , "US state, capital Madision" .)