Also where do you think the CIA gets the authority to “check out” as you call it an American citizen?
Before the CIA can give you a clearance, you have to sign documents giving them permission to vet you for that clearance. Even the FBI needs legal authorization.
A CIA analyst can not wake up one morning and go into his office and decide to “investigative” someone or something because he feels like it. The CIA can no more do this then Air Force OSI analyst can decide to investigate say his neighbor. Every action particularly in the information age leaves an “audit trail” and analysts & field people are constantly “audited” to make sure that every action done & dollar spent is against the “target list”. It is a absolutely career ending and/or prosecutable action if someone should spend time & dollars against something not on that list. To even get time on a “national asset” means many many targeting committee approvals. So doing what you are suggesting wouldn't remain "secret" very long. The person that did this would be very lucky if he was only demoted!
The “rogue” federal agency notion is for spy novels, TV & movies.
No one!
The CPUSA Presidential candidate even when he/she was a the absolute cat's paw of the old USSR during Cold War, if he/she would have actually won. Well then they won, too bad American voter! American voter you should have cared more about the voting franchise then about who is on American Idol!
A voter has great responsibility, candidate character matters ! It's the voter's job to vet the candidate! However I am sure you know that or you wouldn't be on this forum.