This is what intelligence policy oversight is designed to do: http://mattstoller.tumblr.com/post/74403978441/the-secret-government-problem-and-congressional
If you believe policy will stop this, you're a fool.
The US intelligence community oversight system has been comprehensively and robustly designed to prevent oversight from occurring.
They have a very careful playbook for dealing with exactly the problems they currently have, and are executing it well.
The Church Committee was an utter scam, and folks who waste their breath on policy would have us fall for this again.