Ok, I'll accept your analysis of how the division began and progressed...it rather coincides with the acceleration of the furthering of social issues by the left during those years, and the increased pressure the left put on resolving them. A big difference between the left and the right has always been pace, and so I can see how this division grew in direct correlation to the further of social issues, and the resulting pushback.
But I believe Trump was different in the fact that he weaponized the division, or at minimum harnessed it to secure his win. He did not shy away from creating more, rather he put the pedal to the metal, increasingly as the response from the GOP base showered him with approval. This represents a new response to the division that was brewing among the citizenry...again, I'm open to being corrected, but I don't think any presidential candidate approached an election quite like Trump did, with sewing division being a key component of his (or his handlers') strategy to win. By the way, I hated HRC's "deplorable" designation, too, for the same reason. It was an ugly, ugly election.
The "****hole" comment, if it happened, is rather insignificant to me, to be honest... I mean, it's utterly gross, but gross is what I've come to expect. I can't think any lower of the guy, so new infractions are rather meaningless...the worst is the worst, regardless to what you add to it. But, the tastelessness of it coming from the President of the United States of America, is staggering to most folks. It's in the same league as the Queen of England being featured in a bukake film (exaggerating, of course, but hopefully you get the gist of what I'm saying). Regardless of what you or I may think of these countries, it's simply not presidential behavior - note, I'm not even going to debate the racist aspect of it, I'm deliberately omitting it, others have covered it well.
However, Trump's use of cult of personality makes something that *should* be a no brainer become yet another battlefield of contrasting opinions, driving further division between his supporters and his haters. America does not need a leader who drives polarization, they need a leader that will unite them, especially if this has been building for years, as you say. I think it's very reasonable, as well as patriotic, to be frustrated and angry about the impact he is having in this regard, irrespective of what side you're on.
Back to you...