"The United States government classification system is established under Executive Order 13526, the latest in a long series of executive orders on the topic. Issued by President Barack Obama in 2009, Executive Order 13526 replaced earlier executive orders on the topic and modified the regulations codified to 32 C.F.R. 2001. It lays out the system of classification, declassification, and handling of national security information generated by the U.S. government and its employees and contractors, as well as information received from other governments.
The desired degree of secrecy about such information is known as its sensitivity. Sensitivity is based upon a calculation of the damage to national security that the release of the information would cause. The United States has three levels of classification: Confidential, Secret, and Top Secret. Each level of classification indicates an increasing degree of sensitivity. Thus, if one holds a Top Secret security clearance, one is allowed to handle information up to the level of Top Secret, including Secret and Confidential information. If one holds a Secret clearance, one may not then handle Top Secret information, but may handle Secret and Confidential classified information.
The United States does not have a British-style Official Secrets Act; instead, several laws protect classified information, including the Espionage Act of 1917, the Atomic Energy Act of 1954 and the Intelligence Identities Protection Act of 1982. A 2013 report to Congress noted that the relevant laws have been mostly used to prosecute foreign agents, or those passing classified information to them, and that leaks to the press have rarely been prosecuted." wiki
I have several times in the last 13 years sought to explain in these pages the ways that the US government seeks to safeguard secrets. The recent kerfluffle over withdrawal of access to secret information by President Trump makes me think that I should explain it again.
The System. With the exception of nuclear weapons information classified by law after WW2, there is no law that creates protections for secret information in the US, There is nothing equivalent to the UK Official Secrets Act. The system of protections in the US is altogether based on the Executive Branch authority of the president of the US expressed in Executive Orders that are subject to change at the will of the current president. The exception to this being the aforementioned "Q" clearances established by law to protect nuclear weapons secrets, but even these are subject to the president's authority in granting access or withdrawing it. For all other secrets the system is based solely on the executive authority of the president. Federal judges do not have security clearances. Nor do members of Congress. They have access to secret information by virtue of their constitutional office and a presumed need to know. Members of staffs of the Congress and the Federal Courts DO HAVE security clearances and access to needed information as a courtesy granted by the Executive Branch as a constitutional necessity after these staff members are investigated by their granting agencies.
People. Those government employees, prospective employees or military personnel who need access to government secrets of various kinds are investigated with varying degrees of thoroughness before a judgment is made by their employing agency as to their suitability for access at the level required. Such access is granted after the recipient takes an oath to safeguard the information to be provided and signs the accompanying witnessed papers acknowledging the penalties that will accompany an unauthorized disclosure of the information. All of this procedure is executed under the sole and total authority of the president. The president's authority to classify and de-classify is routinely delegated down the chain of command.
Information. The data that is to be safeguarded by these designated people varies dramatically in value and sensitivity. Much of it is classified routinely as a matter of preparing electronic messages from the field. Such preparation is normally done by junior clerks who need a routine that they can rely on in doing their work while their superiors are busy at larger tasks. This results in a flood of electronic messages often classified far above the level of their sensitivity. OTOH there is a great deal of really sensitive information circulating in the government, much of it has to do with the product of information collection operations. Some has to do with policy discussions. Some has to do with design of advanced weapons. Some has to do with proposed or actual military plans. Such information is secreted in compartments of several kinds and is generally know as Special Compartmented Information (SCI). These are the crown jewels of US government secrets. Some people accumulate access to a great many compartments in the course of their duties. People with access to a lot of SCI compartments or Special Access Programs (SAP) are the true grandees of the whole system of classification. Some of these people have information that is of immense monetary or programmatic value to government agencies or to contractor companies serving these agencies. For this reason these people are often allowed to retain access after leaving the government. DoD has a huge program that exists just to manage contractor clearances.
Brennan and Company. As a general practice heads of agencies have been allowed to retain access after departure from government. This was done both as a courtesy and to allow consultation with their successors. This access was and is at the sufferance of the president as the creator and maintainer of the system of clearances and classification.