Excerpts from NBC News:
"Richard Immerman, a historian and an assistant deputy director of national intelligence in the Obama administration, said that, while the president has the authority to declassify documents, there’s a formal process for doing so, and there's no indication Trump used it.
"I’ve seen thousands of declassified documents. They’re all marked ‘declassified’ with the date they were declassified,” Immerman said.
That does not appear to have been the case with some of the documents that were returned to the National Archives from Mar-a-Lago this year. Archivist David S. Ferriero, an Obama appointee, said in a letter to the House Committee on Oversight and Reform in February that his agency had "identified items marked as classified national security information within the boxes” from Mar-a-Lago.
"A source who had discussed the matter with Trump but was not authorized to reveal those conversations said the former president wasn't concerned with formal protocol.
"We’ve told him there’s a process and not following it could be a problem but he didn’t care because he thinks this stuff is dumb,” the source said. “His attitude is that he is the president. He is in charge of the country and therefore national security. So he decides.”
Bradley Moss, a lawyer who specializes in national security issues, said, "That's not how it works."
"Trump could say we're declassifying this until he's blue in the face, but no one is allowed to touch those records until the markings are addressed," said Moss, a frequent Trump critic on Twitter.
"In the current dispute, the apparent lack of a paper trail showing that Trump declassified the documents before he left office could be a problem for the former president, said Stephen Vladeck, a University of Texas School of Law professor who specializes in national security."