There are only three primary classifications (other than "Unclassified") used by the Government:
Top Secret is information which, if disclosed without authorization, could reasonably be expected to cause exceptionally grave damage to the national security.
Secret is information which, if disclosed without authorization, could reasonably be expected to cause serious damage to the national security.
Confidential is information which, if disclosed without authorization, could reasonably be expected to cause damage to the national security.
All other "classifications" are added to one of the three, usually the Top Secret designation. For instance, the Atomic Energy Act of 1954 provides Restricted Data and Formerly Restricted Data monikers that can be added to any of the three. Monikers of this type are usually specific to the type of government institution. In the Army, we used COMSEC, or Communications Security, to indicate that the document or equipment was SECRET/COMSEC --> as with documents that were used to indicate frequencies and callsigns as well as passwords.
The government also uses Need to Know as the basis for all security. Just because someone has Top Secret Clearance, did not mean that they could view any document they wanted, even at the Secret or Confidential levels. They had to have a Need to Know the information.
I would suggest that the President does not have the need to know everything. In fact, it would be a national security risk if he did.