Actually he was exceptionally good as a crook. However, when a crook is caught his sources of crooked income are very reluctant to pay him more largess, they will no longer pay bribes etc. unless they can get a great return for the corrupt investment. That is just the way things work.
I forgot to add, Ray Nagin makes me miss Carlos Marcello. At least the Mafia had standards and rules of business. When they bought someone they stayed bought or else. With Ray Nagin you had to keep buying him time after time. I wonder who really brought him down?