Trump comes across as a man who loves America, Americans and American culture, and who sees the purpose of government as promoting their well-being first and foremost. Say he really believes this, say it's just an act - but it's the image he has.
For Democrat elites, this is unacceptable. American culture is deplorable and shameful - it's something that needs to be apologized for, corrected, and in large part eradicated. Americans are barely much better - way too Christian, way too white. At absolute best, America is something that maybe can become 'good' someday, once the wrong people are eliminated or marginalized.
For Republican elites, this is also unacceptable. Not necessarily because they dislike American culture or the American people, but because they consider both as largely irrelevant. What matters most is a certain set of ideas that they saw as shaping and guiding the policies of certain American politicians and thought-leaders. The ideas are sacrosanct, and how they affect Americans or America is largely an afterthought, or is treated as identical to preserving the ideas. Does America respect unregulated free trade? Then America is doing fine - no need for more details.
You could write whole books on all three claims, and I'll say straight out this is looking at a facet of politics at most, not the distilled truth of it all. But insofar as it applies, consider this: the Republican and Democrat elites aren't necessarily opposed to each other, at least not all of the time. What drives the Democrats are largely factors the Republicans consider irrelevant. Marginalize the Christians, import fifty million illegals, do whatever - the real question is 'Will trade remain free? Will business remain unregulated?', etc. If the answer is 'yes', well, then everything is going to be fine, nothing to be too worried about - things change, after all.
Which is why Trump's rise has been frightening. Trump acts like someone who privileges American culture, American people, and America itself over ideas, and he doesn't think it's in need of some great transformation before it can be called 'good'. Ironically enough, Trump's message is pretty revolutionary in modern American politics, even though the message is at least partly 'We really don't need to change'.
This explains some of the weird trends we're seeing in politics, with Democrats finding themselves supporting Trump rather easily, and some Republicans being viciously hostile. For a lot of Democrats, we really don't need to change. For them, the real promise of the Democrats is 'Americans who are poor or in shitty communities will be helped somehow', and insofar as that's the central concern, America-loving Trump has a message which actually resonates - however he plans on handling it. And for some Republicans, American people are irrelevant - the ideas matter. If America is stronger, if more people speak english, if SJW culture is beaten back... that's fine, but really, it's nothing worth chipping away at free trade or open borders over.