A President has sole authority to declassify documents. He does not have to go thru Other Government Agencies to do so.
FU Bagpipes Barr
Of course, he has, but only as long as he is in office. If Donald Trump had told anyone (= a potential witness) or had written on a piece of paper that he had declassified these documents when he was STILL IN OFFICE, he would have avoided all this trouble.