Having been very badly bullied growing up in school, I do think Trump is a Nelson Muntz like character and a bully. A guy who gets off on deriding and degrading others, but also isn't terribly smart. That said, my experience isn't that bullies will backdown if you tell them no and/or fight back against them. Sure, some will do that. But in my experience, many bullies will just get twice as mad and become more lethal the next time you cross them. They'll torture you until you hit a breaking point and cannot function anymore.
Trump isn't a smart person in-terms of book smarts or general intellect. He's a complete dolt in that regard. He does however have a certain people smarts and understands marketing and selling to some degree, though not in a way he could articulate coherently. Many of the people around Trump are not that smart either, but they understand bullying and submission strategy to a point. They are using him and manipulating him to do bad things and creating lasting damage to our country's democracy and democratic institutions. They are the bullies that come back twice as strong, twice as vengeful, and twice as determined to get revenge on you for standing up to them. It's partly why we see Trump himself and those around him acting so aggressive towards people they view as hostile to their agenda, i.e. the fake new media, academia, scientists, Democrats, etc. It's also why you see them throwing so many different things at the wall in hopes that something will stick and that you can't possibly stay caught up with all the chaos, craziness, and rapid fire changes they are enacting. They are torturing democracy, our institutions, and decent people until we hit our breaking point. Much like many bullies out there.