Revolutionary candidates said to display strength (5)
I believe the answer is:
asset
'strength' is the definition.
(I've seen this before)
'revolutionary candidates said to display' is the wordplay.
'revolutionary' is a reversal indicator.
'to display' indicates a hidden word (I've seen 'displayed' mean this (the answer is displayed within the clue)).
'tessa' is hidden within 'candidates said'.
'tessa' in reverse letter order is 'ASSET'.
(Other definitions for asset that I've seen before include "Something well worth having" , "blessing" , "A thing of value" , "Useful thing or person" , "one liable to be stripped?" .)