Corrupt senator’s crime? (7)
I believe the answer is:
'crime?' is the definition.
(treason is a kind of crime)
'corrupt senator's' is the wordplay.
'corrupt' is an anagram indicator.
'senator' anagrammed gives 'TREASON'.
(Other definitions for treason that I've seen before include "Crime agains one's country", "One rats (anag)", "Gunpowder Plot, say", "Act of betrayal of a government", "Disloyalty (to one's country)".)