Capable Conservative means to apply pressure (6)
I believe the answer is:
clever
'capable' is the definition.
(thesaurus)
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for clever that I've seen before include "Smart, adroit" , "Box ---, outwit someone" , "Deft, able, bright" , "Cute" , "Skilful, adroit" .)