Thus a Communist reached the heights (6)
I believe the answer is:
soared
'reached the heights' is the definition.
(I've seen this in another clue)
'thus a communist' is the wordplay.
'thus' becomes 'so' (synonyms).
'communist' becomes 'red' (red can informally mean communist).
'so'+'a'+'red'='SOARED'
(Other definitions for soared that I've seen before include "Rose high into the air" , "Flew upwards or high in the sky" , "Rose high in flight like bird" .)