Attempt to capture old conservative (4)
I believe the answer is:
tory
'conservative' is the definition.
(informal term for a Conservative Party member)
'attempt to capture old' is the wordplay.
'attempt to' becomes 'try' (I've seen this in other clues).
'capture' indicates putting letters inside.
'old' becomes 'o' (abbreviation).
'try' enclosing 'o' is 'TORY'.
(Other definitions for tory that I've seen before include "Politician; tyro (anag.)" , "English Conservative politician or Donegal island" , "Traditionalist" , "blue" , "A British Conservative" .)