Corrupt vote starts to upset the election (7)
I believe the answer is:
pollute
'corrupt' is the definition.
(I've seen this in another clue)
'vote starts to upset the election' is the wordplay.
'vote' becomes 'poll' (polling is a kind of voting).
'starts to' indicates taking the first letters.
The initial letters of 'upset the election' is 'ute'.
'poll'+'ute'='POLLUTE'
(Other definitions for pollute that I've seen before include "Taint or contaminate, air or water" , "Make dirty or impure" , "Adulterate, contaminate" , "Add impurities" , "inhibit plant life?" .)