Air National Guardsman Teixeira to admit he was Pentagon files leaker

Some people get their TS/SCI clearance before they ever get to boot camp. They just have to pass the background checks. There are also high ranking people with no security clearance at all. Clearance is based on approved designated role and background checks whereas rank/pay is based on time in service and eventually passing tests and training. Both inexperienced low ranking people and high ranking people with a lot of time in service come with their own sets of security risks.