There is absolutely no doubt about this.

I wholeheartedly agree with everything you said.

It’s not so much the act itself. It’s possible that Trump made a “mistake” by reflexively saluting in return like he might otherwise do in any other situation. Again, it’s the fact that had Obama done this Fox News would run the footage 24/7 with headlines like “Why does Obama love the NK military?”, “Obama embarrasses country, some say”, “Did Obama shows more respect for NK than G7?”. Hannity would be in tears lamenting Obama embarrassing us and imagining our country being laughed at. He would probably be suggesting that a real man would have punched Un in the face.

You imply some level of planning and forethought from Trump, which is doubtful. More likely, Kim saw an opening (meeting one-on-one with the US President on equal terms is a massive coup for his regime), threw out the carrot, and Trump took the bait.

If a meaningful change for the better happens, I’ll gladly give credit where credit is due, but so far, aside from Trump giving Kim everything he’s asked for, North Korea has yet to promise anything they haven’t promised before.

Yes, he believes it, and no doubt that belief is being reinforced by those around him given that he’s ditched almost everyone who was willing to tell him the truth.