I’ve been saying these things on Twitter, but I probably should provide a more stationary, all-in-one-place form for those not on Twitter.
Classification is a system for dealing with sensitive information that could harm the United States if made public. It is a system of instructions for handling that information. Information is classified, and documents containing that information are classified. Other materials, including physical models and the usual elaborations on documents like videos, may be classified. I’ll subsume them all under the word “documents.”
Declassification involves declaring the information no longer of potential harm to the United States. Because it is a part of the system for handling documents, it must be made known to the people who will be handling those documents.
Trump seems to believe an essentialist version of classification, that it is an inherent quality of a document that can be added or removed by his mental actions. This is, of course, absurd.
There are two systems of classification in the United States. National Security Information (NSI), which is mostly what is being discussed with regard to the documents taken from Mar-a-Lago. It is also called National Defense Information, which can be confusing because the Espionage Act refers to national defense information. The Espionage Act was written before today’s system of classification was developed in World War II.
Restricted Data (RD) is information relating to nuclear weapons and is defined by statute. It can be declassified only by a legally defined process. There seem to be one or two of these in the MAL documents.
What Trump is saying is gibberish. Someone told him that the President has ultimate power to classify and declassify, but that power is part of a system for protecting information. It is only useful if the others in that system are notified. For example, if Trump has Copy 1 of 5 and he declassifies, he’s declassifying all the copies, and the other holders must be notified. Additionally, there are big books (or I suppose memory cards now) listing what is classified, and they must be changed.
Keep in mind that classification is of information and a way to tell people how to handle the information, and it’s easier to make sense of the issues.
Alex Wellerstein has a much more complete discussion of the issues.