Kepler
Si certus es dubita
Man the GOP really thinks the "he declassified everything" mantra is going to stick...
As somebody in the biz: while classification authority derives from the President via every contractor's favorite Executive Order, EO12333, (pronounced "E O twelve triple three," now you too can be a bloodsucking tick on the American body politic; trust me, it is not worth dealing with the insolence of government staffers, particularly my wife),
1. There is a formal (and time-consuming) process with checks and receipts
2. It is unclear whether the President can declassify just any document, particularly special access program (SAP) documents
3. AND HE CAN'T AFTER HE LEAVES OFFICE!!!
There is nothing magical about being a former President. There are situations in which the intelligence community has permitted certain former presidents to retain certain documents for memoirs, as well as certain clearances for being briefed for new information to advise the sitting President. However, all of that is entirely at the discretion of the IC. The moment Biden was sworn in, Dump ceased to have any more authority to declassify any document than you do.