My understanding from briefly covering this in law school and reading some technical articles about it over the past year, is that classification falls under congressional powers, and the only reason the executive branch has any say in the matter as to documents is because Congress passed laws delegating some of that authority to the executive branch. In no circumstance under the law, can the president simply state that a document is declassified and make it so because no such exists under the statute.

The president has authority to initiate the process to declassify any documentwith the exception of nuclear secrets.

The president could read a classified non-nuclear document publicly, and the subject matter would lose its classification, but not the document itself, until it went through the applicable agency’s legal procedure for declassification.

Trump had not initiated such processes and had not declassified the subject matter publicly while president.

The entirety of the above statement are irrelevant to two things as far as Trump’s crimes: any of Trump’s actions after the lawful end of his tenure and nuclear secrets, to which none of the above applies, as Congress delegated classification of nuclear secrets to our nuclear energy regulators.

Trump also lied repeatedly to the public and law enforcement, and engaged in an open conspiracy to illegally destroy evidence and tamper with witnesses.

By the time this is over, I won’t be surprised if it’s revealed he sold nuclear secrets to the Saudis, Russia, or China. Dude had been a foreign agent since the 80’s.