Trump held on to the documents because he anticipated an opportunity to commit treason

[bpj62]

20. Seditious Conspiracy Yes

Trumps actions on January 6th come down to an attempt to overthrow the Government. That is seditious conspiracy. Treason is the act of giving aid, comfort and abetting the enemy. As we are not at war with anyone at this time, it would be hard to prove treason for January 6th.
Treason is the only crime that is actually mentioned in the Constitution and they did this because of the actions of Benedict Arnold. The founders wanted to make it very clear how they felt about treason.

Now if it is ever proven that he gave/sold secret documents to other countries than you may have a case for treason which is punishable by death.