Trumps lawyers are telling us they have no defense in the secret document investigation.

[FBaggins]

63. I think that's somewhat circular

If a president treating classified information as though it were declassified indicates that he believed that it was declassified... then taking it with him when he left office could be said to mean the same thing.

Indeed... this is similar to what the judge thought in the "Clinton sock drawer" case. In her second footnote, she appears to be saying that Clinton's decision to take the tapes with him was evidence of his decision to consider them "personal" rather than "presidential".

Re: your JFK example. There's no evidence that JFK followed any formal procedure to declassify the information that he chose to share. I think we both agree that the fact that he shared it was enough. I certainly don't think that he could be accused of a crime.

But what if he had "secretly" declassified the rest of that info in the middle of that whole event and sold it to a Soviet agent or to an ally of the Soviets?

There's an argument that this would be an impeachable offense, but not a crime... but it doesn't matter unless/until someone gives us a reason to think that happened. More relevantly, however, is what if he never declassified it by chose to share it with an ally? That happens all the time. It's probably happening in Ukraine right now. But if it's done at the direction of the commander in chief - one could argue that Congress does not have the power to place a restriction there.

So, evidence beyond Trump's very unreliable word that the documents were declassified is important, along with the timing of the declassification and the reason for it.

All logically true... but that's not the same thing as legally enforceable.

It's like saying that Congress should pass a law forbidding the president from pardoning his political allies. They can't do it. They can (and have) make it a crime to trade the exercise of that power for things of value... but they can't remove the power itself - even if it makes logical sense to do so.