Once I let criminal vote (8)
I believe the answer is:
election
'vote' is the definition.
(I know that Election is a type of vote)
'once i let criminal' is the wordplay.
'criminal' indicates an anagram.
'once'+'i'+'let'='onceilet'
'onceilet' is an anagram of 'ELECTION'.
(Other definitions for election that I've seen before include "Time for political change" , "Poll" , "Polling process" , "Ballot for public office" , "The act of choosing for office" .)