As for the president's power to declassify materials, here's some background on how it works, according to current and former intelligence officials familiar with the declassification process.
First, a U.S. president does have uniquely sweeping declassification abilities, though there is a process that involves written documentation and several other steps.
It's not the case that a president can declassify documents with just verbal instructions. His instruction to declassify a given document would first be memorialized in a written memo, usually drafted by White House counsel, which he would then sign.
Typically, the leadership of the agency or agencies with equities in the document would be consulted and given an opportunity to provide their views on the declassification decision. As the ultimate declassification authority, however, the president can decide to override any objections they raise.
Once a final decision is made, and the relevant agency receives the president's signed memo, the physical document in question would be marked — the old classification level would be crossed out — and the document would then be stamped, "Declassified on X date" by the agency in question.
Former Trump administration officials have claimed that Trump previously declassified the documents taken with him to Mar-a-Lago, but that the classification markings had not been updated.
FBI agents seized several sets of records of various classified levels from Trump's home in Florida.
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