First, the scenarios I proposed were not Trump specific, which is why I said “president” and “ex-president”. I wanted to address the general principle rather than the individual.
Second, most of what the article is discussing the classification authority in relation to a sitting president. It tries to extend that to a president leaving office, but I don’t find it persuasive. And honestly, I hope that position is never accepted as correct.
Let me explain why with another scenario. Let’s assume Trump used this as a defense and was able to get an expedited hearing by SCOTUS, and just prior to the election, SCOTUS agrees - any classified information the departing president takes with him is automatically declassified. Trump wins the election! On January 20th, Joe Biden packs up truckloads of sensitive confidential data that China, Ukraine and other countries would love to get their hands on. On January 21st, he sets up shop selling the information to the highest bidder - and there is not a thing anyone can do, because according to the premise you proposed, everything he takes is declassified and belongs to him. He even gives a big chunk to Hunter to set up his own shop selling the data - since the data is declassified, there can be no prohibition on him doing so.
Do you see the problem?
Can you please clarify:
A President leaving office or a President who has left office?
I agree with you that once out of office, a President does not have the power to declassify documents. Is that what is being alleged about President Trump? I don't think so.
As to a President who is leaving office, he retains his powers until 11:59:59 on January 20. Are you saying that you don't accept the position that a President can declassify documents up to that moment?
Regarding your scenario, declassified yes, "belongs to him," no. For your scenario to happen, American would have had to elect a scoundrel, meaning that the entire campaign and election process, plus a term or two of Congressional oversight, has failed to discover the true nature of such a scoundrel. Besides, your scenario is treason, whether in or out of office and would be treated as such.
-PJ