A party left-winger is loved (6)
I believe the answer is:
adored
'is loved' is the definition.
('adored' can be similar in meaning to 'loved')
'a party left-winger' is the wordplay.
'party' becomes 'do' (do is a kind of party).
'left-winger' becomes 'red' (red is a kind of left-winger).
'a'+'do'+'red'='ADORED'
(Other definitions for adored that I've seen before include "Worshipped and revered" , "having lover" , "Worshipped, loved" , "hugely popular" , "Loved dearly" .)