Socialist fiery and very popular (3,3)
I believe the answer is:
red hot
'very popular' is the definition.
(I've seen this before)
'socialist fiery' is the wordplay.
'socialist' becomes 'red' (socialism is often associated with the colour red).
'fiery' becomes 'hot' (synonyms).
'red'+'hot'='RED-HOT'
'and' is the link.
(Other definitions for red hot that I've seen before include "Fiercely glowing" , "Very busy" , "Very keen" , "Strongly fancied to win" , "At a very high temperature" .)