US politician who could resort to treason (7)
I believe the answer is:
senator
'us politician' is the definition.
(the US has a senate)
'resort to treason' is the wordplay.
'resort' indicates an anagram.
'treason' is an anagram of 'SENATOR'.
'who could' is the link.
(Other definitions for senator that I've seen before include "Governor" , "politician going wrong" , "One of 100 on Capitol Hill" , "American politician" , "US politician" .)