The Mueller investigation was cited to President Trump, by Deputy Attorney General Rod Rosenstein, as a specific reason not to declassify certain documents. Here’s a link to the General Principles of declassification [SEE HERE] Yes, the President can declassify anything; however, there is a process that must be followed.
With the completion of the Mueller investigation, it would appear that President Trump could now declassify the documents as requested by congress on September 6th, 2018. Additionally, after the original declassification request, there were other documents added to the list. Perhaps it is worthwhile remembering what those declassification documents are:
♦ The first item(s) is/are the Carter Page FISA applications (including specifically pages 10-12 and 17-34 and relevant footnotes). This request was modified to include the last 22 pages of the third renewal of the FISA application (dated July 2016).
♦ The second item(s) on the original request are all of the Bruce Ohr 302’s, FBI notes from interviews and debriefing sessions, and other relevant documents associated with the interviews of Bruce Ohr and his internal communications. This request also includes exculpatory evidence that Bruce Ohr may have shared.
♦ The third batch of documents requested by congress was: “all exculpatory evidence regarding Carter Page and others, that were presented to the Gang of Eight, but not presented to the FISA Court.”
♦ The fourth request was for the unredacted “Scope Memo”, authored by Deputy Rosenstein, that authorized the specific investigative direction of Robert Mueller. With the Mueller probe ended, there should be no reason to withhold and redact the authorization document known as the “Scope Memo”.
♦ The fifth item is the originating Electronic Communication or “EC” authored by CIA Director John Brennan to former FBI Director James Comey. The two-page EC is the originating memorandum that outlines the reason why Brennan felt operation “Crossfire Hurricane” should be initiated to investigate the Trump campaign (July 31, 2016).
♦ The sixth item on the original request was for the release of the full and unredacted text messaging and communication between FBI Lawyer Lisa Page and FBI Special Agent Peter Strzok. There are thousands of redactions within the previously released text messages; there are also many that were removed. The request to President Trump was for all redactions to be removed and for all previously withheld communication to be provided.
NOTE: Recently it has been revealed there are also text messages between Lisa Page and former FBI Deputy Director Andrew McCabe. I would presume the congressional request would also want those added to their original request for declassification and production.