Highly unlikely this happens very often at all. Counter-intelligence by the FBI (the primary intel agency dealling with domestic political organizations) is very thorough. It would take an extremely skilled person to get through their interviews, background checks, mandatory polygraph tests, etc.
The FBI are the best trained people in the world at eliciting information from people unwillingly/unknowingly - which is enough of a barrier on it's own.
The FBI are the best trained people in the world at eliciting information from people unwillingly/unknowingly - which is enough of a barrier on it's own.