From my experience, and others may differ..degree of security clearance doesn't always rest with pay grade. Bradley (Chelsea)
Manning, was a PFC (E3), when he betrayed his country. Meanwhile, thousands of other E3s, kept their honor.
I was an E3 when I first received my secret clearance...as was my grandson, when he was granted top secret....and he still carries it
in his present job...even though his pay grade now is equivalent to a Major or Lt Col..
Curiously, it is often high ranking people, even as civilians..who have turned to treason. All it takes is some clown who thinks he/she knows better than anyone else. ...Consider Julius and Ethel Rosenberg, both of whom, took a seat in "old Sparky" !
The FBI and others completely investigate all candidates for security clearance. It appears that most all start out fine, but end up snared in some kind of habit or sin that draws them away from their original position.
Just review.. During WW2 Norway minister defense, Vidkun Quisling, turned to the Nazis..now "Quisling" is synonymous with treason.
Phillipe Petain, Prime minister of France, when the war started, caved to the Nazis..forming the Vichy French. the Vichy scuttled off
to Algiers, and held out until the invasion of North Africa..
Then there was chief warrant officer John Walker, who led a family of treason..
...And perhaps the most famous traitor of all....General Benedict Arnold ! If only he had not met Miss Peggy Shippen !
