It's not so difficult to understand. Calling everyone in rural areas stupid in broad strokes ignoring poverty, a lack of opportunity, and, I dunno, basic social etiquette probably hasn't made people like Democrats. Raw fearmongering absent honesty about our actual economic problems explains the rest. They are being lied to, and instead of getting mad about this, to a tee the interactions I've seen between Trump supporters and the rest of America has taken one of two directions: ad-hominem hostility attacking their moral character for supporting Trump, or smug certainty that they'll join up with one of the Good Guys if only they're shown enough facts. There's never any effort to connect first. It's a profound failure in good rhetoric.
I really think the problem with this campaign cycle is that we weren't ready to move it all on the internet. I haven't been paying as much attention to the Republican race, but Sanders still has a pretty sizable phone-banking operation, he's still putting his money on interactions in-person, and he's at his best when his supporters stay out of the internet milieu. Those rallies are important for reinforcing his image as a genuine candidate (and I believe he is genuine), but when we meet up online with Clinton supporters, communications break down and everything gets uglier.
Very few people remember a time when moderation wasn't done on a massive and impersonal scale like Facebook. It's accepted that some sort of etiquette exists, but it's not the etiquette we need online, it's the one we're pulling from real life where public shame rules. A concerted effort to understand that actual people are behind the words we're reading doesn't exist. Instead, absolutely everything is seen as a potential personal attack, or worse, misinformation by stupid/corrupt/old/young/whatever <insert candidate> voters. Absolutely everyone is a "troll" (translation: not a person) Admitting that you're wrong about anything is the ultimate failure - I've tried to do it as much as possible to counteract that absolutism, but yeah...