And his "Louisiana drawl for the role of Jim Garrison in "JFK" was an embarrassment (never mind the fact that Jim Garrison HAD no such drawl and was, in fact, from CHICAGO).
I thought his performance in that film was fine. And, though I'm no expert on the subject, though Garrison was born outside of the state, he spoke with a southern accent in every interview I've seen with him. Oliver Stone makes the same point when he defends this performance, for whatever that is worth.