1. There is no allowable "Vulcan mind meld" declassification technique.

2. The Presidential Records Act (44 US Code Chapter 22) specifically says he could not keep those records and had to give them back.
The text of Section 2202 - The United States shall reserve and retain complete ownership, possession, and control of Presidential records; and such records shall be administered in accordance with the provisions of this chapter.
Text of Section 2203(g) -
(1)Upon the conclusion of a President’s term of office, or if a President serves consecutive terms upon the conclusion of the last term, the Archivist of the United States shall assume responsibility for the custody, control, and preservation of, and access to, the Presidential records of that President. The Archivist shall have an affirmative duty to make such records available to the public as rapidly and completely as possible consistent with the provisions of this chapter.
(2)The Archivist shall deposit all such Presidential records in a Presidential archival depository or another archival facility operated by the United States. The Archivist is authorized to designate, after consultation with the former President, a director at each depository or facility, who shall be responsible for the care and preservation of such records.

3. Oh and can't forget why he was charged under the Espionage Act (pay attention to the end of the subsection)-
Text of 18 US Code Section 793 -
(d)Whoever, lawfully having possession of, access to, control over, or being entrusted with any document, writing, code book, signal book, sketch, photograph, photographic negative, blueprint, plan, map, model, instrument, appliance, or note relating to the national defense, or information relating to the national defense which information the possessor has reason to believe could be used to the injury of the United States or to the advantage of any foreign nation, willfully communicates, delivers, transmits or causes to be communicated, delivered, or transmitted or attempts to communicate, deliver, transmit or cause to be communicated, delivered or transmitted the same to any person not entitled to receive it, or willfully retains the same and fails to deliver it on demand to the officer or employee of the United States entitled to receive it;