When you look at it through this prism, you may start to understand the Trump doesn't have a hard on for seeing the rest of the world fall into chaos, he just realizes -- as do many Americans-- that we cannot continue to be a hegemonic power while our own infrastructure crumbles. That sort of thing destroys nations (most recently, see: U.S.S.R).
I do agree that what Trump is likely attempting to do with his international policy is to look like an unpredictable madman. I believe this is a facade, as one could argue that his national policy has been amazingly consistent, relatively speaking. If I had to guess, in 3-4 years, you'll start to see him become more predictable, and international policy will begin to make more sense. Probably with just enough sprinkling of unpredictability to keep folks on their toes.
Now,to briefly analyze what Obama (and Bush before him) were doing in dumping the trillions abroad, was not to be some altruistic "protector of the free world", let's face it. In a nutshell the policy for the past couple decades (at least) has been to spend American tax money abroad in order to spread our corporations throughout the world. In turn the politicians get to kickbacks, and get to remain in power. It's no coincidence that Hillary spent literal billions on her campaign; where the hell do you think this money came from (certainly not from "i'm with her" shirt-wearing, pussy-cat-hat wearing millennials!)? But I digress, and the obvious problem with this sort of global corporatism, is the majority of the benefit never comes back to the average Joe citizen, unless they own stock in said companies.
To take it a step further, you don't even need to put on a tin foil hat to understand that the media is controlled by said global corporations, and are kicking and screaming to make it look like the what Trump, and the U.S., is doing is all ape shit crazy, when really it is the opposite. What Trump is doing is completely fucking sane, and probably the only sane thing we've done in the last couple of decades, international policy-wise.
All that said, I do appreciate how we can have a discussion here with folks from all over the world, and think it's amazing to hear different global viewpoints.