I’m saying that the only reason he should have resigned was for being an idiot and forgetting he wasn’t on stage. You take a job for a government official, you do not go on social media and crack jokes on an account that can be linked to you. Pure stupidity to do so.
The “fair game” was explained in my comment, imo. However, it means that the target and subject matter of his bad joke were not, and should not be considered protected under normal circumstances. Public figures are subject to different standards regarding comedy, it’s just the way it is. And there’s no subject that’s totally out of bounds for humor, it’s all about how it’s used.