POTUS needs to be diplomatic, agreed. However the politics only really comes into play domestically because as far as the constitution is concerned, POTUS has no competition when it comes to representing the US. That said, Trumps "style" of diplomacy isnt really a style. He has no style, like he has no real plan, like he has no core values. The guy is a builder and by definition he follows the winds of opportunity in search of a buck. I'd venture to say that this is probably the first real job he has ever had. And that he lacks the life skills to figure it out.
That said, I can make the same argument as to why the college professor/community organizer Obama also lacked the life skills to do the job. But he at least had skin color, a fawning media, and a more eloquent speaking style (meaning that it sounded better even when he spoke with his foot in his mouth).
The last President that had any executive experience was W as gov of Texas. Heck his leadership of the Rangers was far better preparation for POTUS than anything we've had the last 10 years. If that doesn't make you say WTF....I give up, lol!