When the president gets away with all sorts of crime. When he openly mocks people. When he indulges in racism. When he complains about being treated unfairly. When he lies. When he defrauds, or grifts, or flip-flops. When he's misogynitic. What's he saying is "you too can do these things and get away with it".
People like that. People like that there's no accountability for bad behavior.
Sure, we can talk about policy, or economy, or whatever (how's that working out?) But deep down the democrats ask us to be the best version of ourselves (or else) and Republicans delight in us being the worst.
Human nature being what it is, we end up here. Just remember folks, we voted for this.
I think what it comes down to is that the average person in our society is just an aggressive basic shithead who isn't burdened by an abundance of thinking, and so to them Trump appears as a successful businessman rather than a hollow snake oil salesman.