Name the deviant Tory to ruin (7)
I believe the answer is:
destroy
'to ruin' is the definition.
('destroy' can be a synonym of 'ruin')
'name the deviant tory' is the wordplay.
'name' becomes 'des' ().
'the deviant' is an anagram indicator.
'tory' anagrammed gives 'troy'.
'des'+'troy'='DESTROY'
(Other definitions for destroy that I've seen before include "Obliterate" , "Ruin or defeat roundly" , "Completely ruin" , "Ruin; pull down" , "put to death" .)