When you are as extreme as Bustamante is and can still tie down a major chunk of your party as he has, there isn't much in the way of a PR hit that can hurt you. Everyone in the RAT party already knows how extreme he is and wants him anyway. What can hurt him? Finding out that he secretly reads the Wall Street Journal Opinion page or National Review? Did he praise Bill Buckley at some occasion in the past?
Nope. His opposition needs to coalesce. Nothing more is going to syphon any votes from him, it will be up to his opponents to decide that beating him is priority #1.