Yeah, and because the framers of the Constitution themselves also didn't think of such a thing or believe it was necessary, if anyone now ever did try to pass a law that makes it illegal for a president to attempt to overthrow the government, the Supreme Court, depending on if they're feeling particularly dumbshit (like, say, the current SCOTUS, for example), could very well just go "Welp, the Constitution doesn't say that. ¯\_(ツ)_/¯" and strike down such a law.