Please point to the written procedure the President must follow. I haven't seen it.
Yes, designated by the Originating Authority, the PRESIDENT. That ruling applied to everyone else except him.
Presidents de facto declassify materials all the time. Simply the action of removing classified materials from the White House secure areas to the private quarters, de facto declassified those materials (at least temporarily). Biden has admitted he took classified materials to the private quarters (which is not a SCIF) on numerous occasions.
You asked: “Please point to the written procedure the President must follow. I haven’t seen it.”
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There isn’t one. The ABA is wrong.
Something that actually happened: In one of his political speeches, President Carter blabbed some classified information on spy satellite capabilities. If anyone else had done that, prison. When President Carter put the classified information on the air, that information was automatically declassified on authority, J. Carter, President of the United States. I have never seen any indication that he did it on purpose. As best I can tell, it was just carelessness. But it is definitionally impossible for the President to commit a crime by revealing classified information. A president can declassify anything, without even meaning to, by revealing it.
(By rumor, this set off a scramble in the classified world, to try to figure out what President Carter had just declassified, and what was still classified.)