Trump has had a hard time picking cabinet members. (Flynn. Sessions) I assume he's better at business.
The way I understand it is that Bannon rode the wave in, got close to power and thought it was his. He became increasingly obnoxious 'til Trump said: You're fired!
If Trump backs out on the wall the left will fill the streets in a world of gloat. Trump would be reviled by everyone.
I predict this will be too much for some members of the right and it will get messy because at that point the right has nothing to lose.