Don't know how they work now but used to be it was for a specified time unless there was a reason to pull it. A carry over period so they didn't have to go through the vetting process again (6-8 pages to fill out and they talk to everybody, secretly). For political appointee or elected official, no reason to continue it. The problem now is the same as watergate, top officials releasing sensitive data to press. Still don't understand why they let Lee go after they caught him selling nuke stuff. These guys presently have no official capacity and everything (classified) they know is still restricted. Illegal to discuss it - period!! Classified material is eventually reviewed and can be DE-classified.