@Zinnia #167950
SCI isn’t actually “above top secret”, but is rather particular documents which are designated to be handled in extremely strict fashion, inside only a contained area (SCIF, or Sensitive Compartmentalized Information Facility), a designated location in many bases and government offices which are very tightly secured against intrusion. SCI documents are generally meant to be viewed in special briefings, copies may be made (but the SCI copies do NOT leave under any circumstance, only approved and documented copies of them). I’m pretty sure following the briefing, they’ll be destroyed in the vast majority of cases (though @KeithInc. might be able to answer that better).
All that said … even having a high enough clearance isn’t enough for most people to actually see the documents. Even someone with top secret clearance has to actually apply for access to specific documents, and has to show some reason they actually need it. Even a captain/colonel in charge of a ship/base cannot simply access all secret/top secret documents, even about their ship/base. The Office of the President, however … has special considerations. Though I’m sure a number of things are still withheld, from any President, they do have access to pretty much anything, and have to have that access.
I don’t doubt in Trump’s case, there was plenty more than usual specifically withheld from him, and because he tends to surround himself with sycophants barely more aware of general human behavior than he is, it was probably pretty easy to do.