Most Powerful Person On Earth

The visa consulate at the US embassy is the most powerful person on Earth. He has the power to over people's life like no other. He can deny the visa and get away with it by not even giving a reson. And applicant don't even have right to appeal. So, one day if he wakes up on the wrong side of the bed, then he can deny everyone's visa that day. To US government, I ask you, how are you ensuring that he is following the correct protocols and not abusing his power?