A President has the ability to declassify it. PERIOD!
Here is the thing, everything is over classified. The intelligence services do this to hide their bullshit and corruption. It helps them from being prosecuted for their crimes. Same way there is always an investigation that goes nowhere to keep the public from knowing about their dirty dealings.
In public hearings how many times do they say, "I am sorry that is classified information so I cannot divulge it here" or "I cannot comment on an ongoing investigation"?
It is how they shut **** down and keep the public from knowing how fvcking corrupt they are.
Raid every single president and you will find documents that are labeled classified. Every single one except maybe Carter.
It is expected for presidents to take tons of documents for their future libraries. Classified documents always get mixed in. This is not the case with vice presidents or their sons.