The reality is that his position hasn't changed, the situation did. The idea that we made great concessions to North Korea with this deal is ludicrous. Obama gave away the farm for very little from Iran and the media want to give him yet another Nobel Prize (to go with the one he got for being black) and what has Trump given up? The suspension of a dog and pony show and a photo op.
The reason that Trump's approval ratings are creeping up is that despite all the media pearl clutching about the proper way to do things the sky isn't falling and he is actually getting things done where traditional methods failed. I don't like Trump and doubt I ever will but attacking him for breaking the mold is a loser strategy and explain why Trump is more trusted than the media. The left has created these fairy tales about why Trump won but they are too invested in their personal word views to accept the simple reality that people are tired of status quo and elected him to do just that. Same reason why Bernie almost beat Hillary and so many of his supporters refused to get behind her.
People want change and they are tried of the same BS. The media has spent to much time and energy selling that BS and building their own little siloes of ditto heads to be part of the mold breaking. They thought Obama was breaking the mold because he had darker skin then previous presidents which is yet another example of their blinders. At some point they will have to accept he is winning and change track or they will fade away.