When I was young, my maternal grandmother was my ally in battles with my mother. ("The enemy of my enemy is my friend.")
Also, my grandmother hated mayonnaise, which my mother liked. Curiously, at about the age of five, I discovered that I hated mayonnaise as well.
In my twenties, with my grandmother in a nursing home, and no longer an effective ally, and with me living on my own, no longer so subject to my mother's whims, I reluctantly tried mayonnaise again. (Someone served me a sandwich already containing it.) Much to my surprise, I found that I loved mayonnaise!
Still, it was not until many years later that I saw what may already be obvious to you: "hating" mayonnaise was a weapon in my battles with my mother, and way to cement my alliance with my grandmother. (Who knows? Perhaps my mother actually hated mayonnaise, and only pretended to like it to bother my grandmother!)
The entire time I "hated" mayonnaise, I never suspected that I was not simply expressing my honest feelings about a food. In short, I was biased against mayonnaise, disliking it for reasons having nothing to do with mayonnaise itself, but which served my self-interest in some other way. ("Other" than avoiding a food I truly didn't like.)
This mechanism is not only at play in children. Let us say that John is a software engineer at a hot high-tech company in California. Let us further imagine that he holds a number of views that more closely align with those of Donald Trump than those of Hillary Clinton: perhaps he is skeptical of free trade, thinks that Russia is not necessarily our enemy, and that nation-building in the Middle East is a terrible idea. (Note: By choosing this example, I am NOT saying this phenomenon only occurs in Clinton supporters: someone living in a mining town in West Virginia who otherwise would be inclined to support Clinton will be just as likely to "discover" reasons they really support Trump.)
But pretty much from top to bottom, and especially top, everyone in his company despises Donald Trump, and regards anyone who would support him as a racist moron. Will John support Trump?
Unless John has an extremely high degree of self-reliance and fortitude, and maybe also a large trust fund, the answer is almost assuredly "no." But what's more, John will convince himself that the reason he, too, despises Trump has nothing to do with the climate of opinion at his company. To admit that it did would wreck his self image as an independent thinker who makes up his own mind on issues based upon evidence alone.
Instead, he sincerely will be convinced that, for instance, Trump's (very poorly put) comments on illegal Mexican immigrants* are sound evidence that Trump is a racist who hates all brown-skinned people. And it will be just as hard to convince him that this makes no sense as it would have been to convince me, at age ten, that I really liked mayonnaise just fine.
And let me reiterate that I absolutely am not suggesting that only Clinton supporters exhibit this phenomena: I focus on them only because, in the circles in which I move, Clinton supporters outnumber Trump supporters by about ten or twenty to one. Thus, I am more alert to the anomaly of the person whose views seem closer to Trump's nevertheless absolutely despising him than I am to the reverse situation.
* I think the way Trump phrased his infamous "they are rapists" remarks was either:
1) completely idiotic; or
2) a calculated effort to be inflammatory and thus attract attention.
Neither option puts Trump in a great light, although 2) might be partially excused as, "well, that's what it takes for an outsider to break through."