Criticise all the candidates (5)
I believe the answer is:
slate
I believe this clue is a double definition.
'criticise' is the first definition.
(I've seen this before)
'all the candidates' is the second definition.
(list of electoral candidates)
(Other definitions for slate that I've seen before include "Grey stone; tab" , "Grey metamorphic rock" , "Run down" , "Roofing plate" , "Scold; hard rock" .)