Doctor gets Conservative backing to reveal decay (3,3)
I believe the answer is:
'decay' is the definition.
(I have seen 'Decay of timber ' mean 'dry rot' so perhaps 'decay' could also mean 'dry rot')
'doctor gets conservative backing' is the wordplay.
'doctor' becomes 'Dr' (abbreviation).
'gets' is a charade indicator (letters next to each other).
'conservative' becomes 'tory' (informal term for a Conservative Party member).
'backing' is a reversal indicator.
'tory' reversed gives 'yrot'.
'to reveal' is the link.
(Other definitions for dry rot that I've seen before include "Fungus affecting wood" , "Wood-destroying fungus" , "housing problem?" , "Disease of wood not well ventilated" , "Decay of badly ventilated wood" .)