Yes I worked in a SCIF in a number of locations even mobile ones. In fact, if the government confiscated your current residence, they could turn a portion of your house into a SCIF by meeting certain requirements.

I am 100% certain a multi-million dollar mansion could be made to meet said criteria....

If he declassified it, wouldn't the classified markings been removed?

It depends on how its done.

As the SC said and Obama's EO expanded on, the President IS the authority. He can do it a number of ways. For example, if Joe is on Air Force 1 holding something that is "classified" and says, "this is bullshit, this shouldn't be classified", then it is so and he can take that original and take it home, hand it to a reporter, his wife, whomever.

Or, he can write a memorandum to declassify documents not currently in his possession in which they would go through a process to remove markings because "normal people" would be handling it at that point and they do not have the authority a president has and thus, follow their documented rules based on their current organization.

Also a number of other ways.

He can even point at a box of "documents" and say "those are declassified" and take them home. He can literally do that.

Wouldn't it be reasonable to expect the FBI to contact whoever classified the documents and ask "Is this material still classified?"

I think it would make more sense to ask the #1 authority as per the constitution, supreme court, and the freshly minted Obama EO....

So you ask Trump even though he's been out of office for two years? Makes sense.

IF the question was did "HE" declassify them seems like that is where you start....

If your wifes car has a dent in it, do you call the insurance company and ask them what happened?

I think you start with the reporting that the documents were marked as classified. I think it's then up to Donnie to prove beyond a reasonable doubt that he declassified them.

Again, per the Supreme Court on this, all he had to do was utter the words.

None of you goons have been able to disprove the Supreme Court Judgement. BLACK AND WHITE!

That's utter bull shit. Why have classification markings at all? All a POTUS has to say is I said those were declassified months ago? Does the SC ruling require that there be witnesses to support those allegations?