Bannon more than any other person steered Trump onto the ideological course that got him elected, and he has done his best to keep him on that course. With Bannon gone and Trump's relations with Sessions worse than ever, most of the advice Trump will get will be from "moderates", establishment Republicans, and his own liberal family members.
I like Bannon, but I disagree with the way you characterize him. Trump was a juggernaut long before Bannon joined his campaign last August. If there is one person in Trump’s campaign who deserves the most credit for his victory (and this is a big IF), I think it’s Kellyanne Conway.