As Josh Marshall wrote he expected him to do it earlier but it was being so disrespected at the Nato Summit and the G-7 by both Angela Merkel and Macron that he lashed at to "punish" the Europeans . Hence the line about respecting Pittsburgh and not Paris.
In addition, Marshall does not think Bannon would have won on this issue if Trump wasn't scared and afraid that the Russian investigations are closing in on him. And as they do, expect Trump to be more reactionary and to unleash repressive policies because he has to grab his base because there is no one else left who support him.
He is being very insecure and as David Brooks said ,"I don't know what psychological issues he's dealing with but I wish he would stop."
A side note, the Washington POst has EPA head Scott Pruitt moving to the front of the line as the most powerful spokesman for the Trump decision. That's good news because Trump can't stand someone getting so much media attention. So he will have to be cut down to size.