The documents case is legally solid, although others like Berger, Petraeus, and Clinton violated classified requirements without prosecution.
Sandy Berger - Clinton's National Security Advisor - stuffed his pants with classified documents from one of those clean rooms and got away with the slap on the wrist. Prosecuting Trump feels challenging, given past leniency for similar cases.
So the arguments seem to be:
Other people have mishandled / taken classified documents in the past, and not this much has been made of it. Indeed, both Pence and Biden have recently been 'caught' in posession of things they shouldn't have. But here's the rub, everyone else, when notified, gave them back. What they did not do was have their lawyers lie about giving docs back, deliberately moving docs ahead of the FBI coming to get them, potentially asking an aide to flood a pool to destroy evidence and oh yeah get caught on tape showing military secrets to a random group of fans. Otherwise same thing.
2. Trumps actions in inciting the Jan 6 riots are unprecedented, and on untouched legal grounding, so maybe we shouldn't bother cause it's hard. Hell of a legal mind you've got there.
3. We can never truly know the inside of another human beings mind, and this crime (like a huge number of them) require that. So again, let's not bother. Nevermind you literally have Trump talking about the 'other guys' problems' on issues he didn't want to deal with which Biden would have to when President, or the countless witnesses acknowleding he knew he'd loss. Again, this is very common in the US legal system. I agree, it's not a slam dunk, but it's also not some crazy theory.
Finally, Georgia is the one. On tape, asking for votes to be found from a person in position to find them. I can't remember the wording, but it's almost a text book example of breaking that law, and simply asking is a crime.
He's an awful human being, a terrible criminal and keeps doing crimes (did another one today, huzzah!) therefore he should be tried and found guitly as a criminal.