Politician capable of treason? (7)
I believe the answer is:
'politician' is the definition.
(I know that senator is a type of legislator)
'of treason?' is the wordplay.
'of' indicates an anagram (the answer comes from or 'of' the letters).
'treason' anagrammed gives 'SENATOR'.
'capable' is the link.
This may not be correct. It may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for senator that I've seen before include "Member of upper house commits treason?" , "Clinton, perhaps" , "Treason committed by member of Upper House" , "Politician involved in treason" , "Legislator -- treason (anag)" .)