Idea: He took the documents because he considers the Presidency to be his personal possession
The documents help assure him he is still the real President in his own addled, self-centered mind, even though I'm sure he knows he lost, he could never accept losing, as Mary Trump has stated. The possession of the documents are to him "proof" he is the real President and that he "owns" them. He clearly has a strong sense of ownership from Mary Trump's book. Why nuclear documents too? Because only a real President could have access to such things in his childish mind. They are a talisman.
Since he thinks they belong to him, I could envision that he could sell them at some point as a matter of course, but don't think that is the main reason.
A question is would he attempt stupidly show off by gifting some secrets to US enemies who he considers to be friends like N Korea's Kim-- that would not be beneath him. Showing off is his secondary motivation IMO.
Evidence here-- it's a small leap for someone like Trump for the idea as to his believing he owns the documents, to the idea he owns them because he remains President.
He's a mental infant. He's a major fucking asshole.
end of story. the rest is gaslightling.
donnie didn't believe any of it was his "personal property" in the sense that he had a legal right to do it within the existing system. of laws.
donnie believes in a system where he can do whatever he wants and "laws" are for other people. i.e., that he could get away with it.
it has a basis in a child's sense of ownership. That's not to say he doesn't use the legal system to attempt to gt his way.
The damage he has done to national security is likely going to take years to address.
Greed - sell the documents
Vengeance - use the information to take down enemies.
He took all that other stuff because his sense of entitlement is absolute. Plus, what he doesnt want for his personal scrap book he can sell to the highest bidder, i.e. Iran, Russia, China, or the Saudis.