Revolutionary's endless poetry of defeat (7)
I believe the answer is:
reverse
'defeat' is the definition.
(I've seen this before)
'revolutionary's endless poetry' is the wordplay.
'revolutionary' becomes 'red'.
'endless' means to remove the last letter.
'poetry' becomes 'verse' ('verse' can be a synonym of 'poetry').
'red' with its final letter taken off is 're'.
're'+'verse'='REVERSE'
'of' is the link.
(Other definitions for reverse that I've seen before include "Change" , "One side of a coin" , "Move backwards" , "Transpose" , "Back (of a coin or medal)" .)