We expect Trump to respond when attacked. It’s what got him elected. Why change what works? It’s not like you’re going to suddenly support him whatever he does.
This is a little different than a normal attack. Steve Bannon was, until a few months ago, a pretty trusted confidante, and even up to a month ago, was still sufficiently close to the President to be able to call him up and ask him to throw his support openly behind Roy Moore.
It’s true that we can expect Trump to respond to an attack with an attack. The Trump side of this equation isn’t the least bit surprising. It’s the Bannon side that’s shocking. My personal theory is that Bannon wants to drive Kushner out of the White House, or more generally, politically sever the President from his family. It’s not just Kushner he wants out of the White House, he wants to make sure that Ivanka and Donald Trump Jr. are also gone. My theory goes further to suggest that because the Kushners are, no matter what official colors they might be wearing now, still basically New York Democrats, Bannon’s world view makes them the enemy, and if they are no longer in a position to politically advise the President, then he will return to Bannon’s righteous cause.
I admit it’s just my theory, and I’m not going to stand on principle and declare it the absolute truth. Another possible explanation that comes to mind is that Bannon is afraid that Congress and/or Mueller might subpoena him next, so he’s making a pre-emptive strike to demonstrate that he has nothing to do with any Russians (and that’s the other part of what we know Bannon made pretty clear to Michael Wolff). I dunno, maybe this theory makes more sense than my first one. There’s certainly a kind of “rats fleeing a sinking ship” feel to the Oval Office these days.
A third theory, which is the most mundane, is that Bannon is nuts. That’s the White House line, but at the same time, considering what happened in Alabama a month ago, it’s pretty clear that Bannon is not only not a “player”, he’s about the furthest thing from a coherent and functional political strategist as one can imagine. Bannon has spent a good deal of time building up a reputation as some sort of right-wing revolutionary who is going to remake the Republican Party, and yet other than getting Trump elected (and honestly, I put that victory on Kellyanne Conway way more than Bannon), and the Alabama catastrophe has stripped him of most of that luster.
Or maybe it’s a bit of all three. Maybe it’s a bit of revenge for Trump picking the Kushners over him, and maybe it’s with the hope that “freed” of the Kushners, Trump will return to the Bannon Way, and while he’s at it, Bannon wants everyone to know he at least didn’t talk to any Russians, and ultimately, surrounding all of it is Bannon’s delusions of grandeur.