I read a book Underground Bases and Tunnels which discussed there was an 'unelected' government that runs over several presidential terms regardless of party status, Demo or Repub. This has been going on for a long time.
It makes sense though in my opinion because if all chains of power were wiped out in say a nuclear attack on Congress, you could get either the army
take over in a bloodless coup, in which case it becomes a military state.
This secret government would be able to come out and pass orders and keep the chain of command and government running, and keep the country going. It
is an excellent back up plan to have in case of any disaster.