This specific scenario with classified documents actually explicitly prevents a person from holding office in the US, it’s section B of a specific statute (I’d have to find it again).Sounds like even a convicted felon is still eligible to run so short of him being in jail there won't be anything stopping him. Seems unlikely he would win again but as we've seen he can inflict serious damage if he wants to.
I’d caution Democrats from convincing themselves that Trump’s support (and therefore chances of winning election) has waned. Trump is merely the vessel people put their discontent into. Trump or not that anger and “fuck you” mentality is growing stronger every day on the right. If it were to be paired with a *competent* fascist like a Tom Cotton, Trumps presidency would look like “the good old days”.