Trump has, to mind, simply presided over a process that's been developing for a long time. He may well have brought matters to a head, just as did Mikael Gorbachev Boris Yeltsin in the USSR, but the damage is now done it's beyond the abilities of any subsequent president to repair.
It seems like you added a lot to your post after I started my response!
On one hand, Trump was obviously riding a wave of DEEP resentment among white, conservative Americans. Right wing media exploded in the USA after Nixon's impeachment. We've always had a deep anti-intellectual bend, but that started to grow the problem a lot over time. In that respect, the election of someone like Trump was likely to happen at some point.
On the other hand, I do think a lot of outside observers are still underestimating just how much destruction Trump personally to our institutions in terms of their ability to actually function. I've seen a lot of people make very handwavy remarks about how the US was clearly going to fall eventually and yadda yadda, This was the difference between "you'll die one day" versus "I just shot you in the stomach!"
The War on Terror in general, and Iraq in particular, destroyed most allies' enthusiasm for joining the US in foreign wars, and Guantanamo Bay and extraordinary rendition to black sights (i.e. torture) did huge damage to the confidence of confidence in the US -- I know for a fact that British and Canadian army officers, some of them pretty senior, were very worried about handing over Iraqi POWs and civilians to the US because they feared it could lead to their prosecution for war crimes under their domestic military and civilian law.
Yes. I think right after 9/11 there was a period of several years where most Americans were completely ready to embrace fascism.
That did calm down for a time which lead to Obama getting elected, but the huge undercurrent of white hatred I mentioned above certainly didn't just vanish. Politically we were doomed, I agree with that. But in terms of the government's actual ability to function, I think the US Military that took Baghdad in 2003 was a radically different (if still flawed) institution than the one that can't stop it's warships from drowning in poop and running out of missiles.
I don't want to get too side tracked on US politics on the CANADA thread! Long story short that we both agree on is that trusting the USA with much of anything would just be unforgivably stupid at this point. That seems to be one of the biggest things Canadians can agree with each other on, and they are correct.
I'm also a bit worried Canada could get attacked by the most broken military ever to be so expensive!