Democrat is leading business party (5)
I believe the answer is:
disco
'party' is the definition.
(I've seen this before)
'democrat is leading business' is the wordplay.
'democrat' becomes 'd'.
'leading' is a charade indicator (letters next to each other).
'business' becomes 'co'.
'd'+'is'+'co'='DISCO'
(Other definitions for disco that I've seen before include "Style of music/dancing" , "Modern dancehall of youth" , "Party with records" , "'Genre of dance music, popular in the 1970s (5)'" , "One might get down to this" .)