That statue is undoubtably on private property- so unless it is his property, his first amendment rights really dont apply.
I wonder had somebody had shot him off the statue, what level of charges would the killer face. My guess is that the "fighting words" doctrine might apply.
Even if they dont apply in the formal sense, it might be very difficult to sit a jury of 12 willing to convict for first or second degree murder. Manslaughter might be a possibility. Though, in east Texas, the conviction might be more towards disturbing the peace, or firing a weapon in city limits.