Socialist joining a party is idolised (6)
I believe the answer is:
adored
'is idolised' is the definition.
(I've seen this before)
'socialist joining a party' is the wordplay.
'socialist' becomes 'red' (red is a kind of socialist).
'joining' means one lot of letters go next to another.
'party' becomes 'do' (do is a kind of party).
'a'+'do'='ado'
'red' after 'ado' is 'ADORED'.
(Other definitions for adored that I've seen before include "enjoyed very much" , "Loved dearly" , "Much loved" , "Doted on" , "Cherished" .)