Caricature of crackpot capturing a politician (7)
I believe the answer is:
lampoon
'caricature' is the definition.
(I know that lampoon is a type of caricature)
'crackpot capturing a politician' is the wordplay.
'crackpot' becomes 'loon' (I've seen this in another clue).
'capturing' is an insertion indicator.
'politician' becomes 'MP' (Member of Parliament).
'a'+'mp'='amp'
'loon' placed around 'amp' is 'LAMPOON'.
'of' acts as a link.
(Other definitions for lampoon that I've seen before include "Piece of writing that ridicules someone" , "Pool man (anag)" , "Burlesque" , "Written ridicule of polo man" , "Literary satire" .)