Even when he was president, Donald Trump lacked the legal authority to declassify a U.S. nuclear weapons-related document that he is charged with illegally possessing, security experts said, contrary to the former U.S. president’s claim.

The secret document, listed as No. 19 in the indictment charging Trump with endangering national security, can — under the Atomic Energy Act — only be declassified through a process that by the statute involves the Department of Energy and the Department of Defense.

For that reason, the experts said, the nuclear document is unique among the 31 in the indictment because the declassification of the others is governed by executive order.