He may have sworn not to divulge secrets, but that does not compass crimes that some would like to keep secret.
He did not “just follow orders”
I am always torn between the public service leaks like this produce..much much better than say stealing nuclear secrets and selling them..but on the other hand the letter of the law states this is a high crime. Argue what we will about the morality of this NSA stuff, no one and no court has really said it is unconstitutional. Therefore I suggest a compromise. Grant him partial immunity and allow him to testify, charge him with a misdemeanor with time served and lets get to the bottom of this cess pool.
I think that is the main concern of Oath Keepers, contingency planning when given unlawful orders. And knowing when you've been given an unlawful order is a problem because many people don't know the Constitution that they've sworn to protect and defend.
“Unit, Corps, God, Country” and arguments about the appropriate order of these priorities comes to mind.