Can a President.. or more importantly a former President declassify any document??

[gratuitous]

25. I take my cue from Cheryl Rofer

She did a long form post at Lawyers Guns and Money on Tuesday. It's worth the time to read through this account by someone who has actually handled and worked with classified documents. The final paragraph addresses the declassification of documents by the President (a former President has no power to do that):

Coda: We will now go through the “Actually, the President holds the ultimate classification authority” stage of social media. This is not untrue, but the way it is used is almost always misleading. (The clue is “actually.”) Even for the President, a certain amount of paperwork and justification is required to declassify classified material. And after noon, January 20, 2021, Trump no longer had that authority. If he had documents with classified markings at Mar-a-Lago, he was in violation of the regulations. Whether it was a crime depends on the level and type of classification.

Which means that on his way out the door at 11:59 a.m. on January 20, 2021, the former guy couldn't just wave his little hands over the contents of the last U-Haul and say, "I de-classify thee, I de-classify thee, mea maxima de-classify thee" and have done with it. There has to be a record of that declassification, otherwise the other people with access to those documents don't know how they are to be handled.

The former guy and his minions would like everyone to believe that de-classification of documents is like the old Harlem Globetrotters "time out, time back in" gag, where Meadowlark Lemon would call time out to get his defender to relax his guard, then call "time back in" and fly by him for a lay-in. But that's not the way it works.