He can say many things that are negative about an elected official, as long as he doesn’t do it in an official capacity.
In an official capacity, he can state that he will not follow unlawful orders. Now that certainly begs the question, but as long as he doesn’t close the loop, he would be fine.
If YOU want to take the chance to open you mouth and say something in public negative like this, then YOU’d better be prepared when your command brings you up on charges! Is THAT worth it? Losing your career over? For a piece of slime like him. See, I am retired, so I can now say all I want. Short of threatening stuff.