Trump thinks he is an attorney, apparently. Maybe he should try to get a licence.
Last time I looked, Comey released non-classified information that was subsequently reclassified as confidential. The usual rule with these sorts of things is that you are liable only for breaches of law that were breaches obtaining at that time. Retroactive law is a no-no. I imagine the same applies to documents.
Not only that, but you can't make a document confidential that was already released. So it's absurd on its face.
If there's a case to make, I will be curious to see what it is. But it would be done by an attorney, not by a president. Indeed, the notion that a president is pressuring legal people to act against his opponents is yet another breach of the rule of law.