Tin foil hat time!

Bannon is the white house leaker.

Why?

1) The more paranoid Trump gets the easier he is to goad. Based on the rule of using people's anger to control them. Bannon is the Leaker.

2) Trump gets most of his news from brietbart. Take for example his recent foray into authoritarianism with the accusations against Obama.

3) The fewer Trump's sources of information are, the easier it is to control the message that you want. As an advisor and Brietbart owner he makes the echo chamber.

4) By having a weapon to use against rivals Bannon can remove them when they disagree ideologically or become a competitor that challenges his power.

5) Look for what is absent. Bannon has not yet had anything leaked on himself. The newest target is Kushner which may be an attempt to reduce Ivanka's influence.

6) Bannon is at heart a cocky bastard and wants control. You don't get to be the head of a media company without interest in propaganda, manipulation, ect. He is the only one who had this as an interest. Had he kept up with his reading he would have leaked something small an inconsequential on himself early on to redirect suspicion.

How to test the theory? If Bannon is removed from his role due to a leak it isn't him. If not, and he remains the only starting advisor it is him.