Here's the short of it - Trump has so many supporters because he is saying exactly what they think. They don't support him despite the racism and sexism and all that - they love him because of it. They say they don't, because they would be embarrassed to admit it, but they do.
Because really, if I supported a candidate and believed is his or her positions on the issues, and then s/he made fun of a disabled person or pretended not to know who David Duke is or called women s/he didn't like fat and ugly...that would end my support. Immediately. Hard stop. Trump's supporters only love him more the more extreme he gets. They love it and they support it and it's what they want.
Americans are scared because life is hard. They feel like their power is slipping away, and who better to blame than the "other"? Donald Trump makes them feel like he is their big strong daddy who will send the bad guys away with just a stern look and snide comment. And Americans want to believe this. They do believe this...as if life were that simple.
I have to admit, I do not know one person in real life who supports Donald Trump. No one I have actual live conversations with has any idea why anyone is supporting him. But numerous people I know (and a distant cousin or three) on Facebook are loud-mouthed supporters of his, and if you try to engage politically about him, they all-caps scream at you. I don't know if they learned to shout down their detractors rather than converse with them from Trump, or whether they are just birds of a feather. But they certainly have the lack of intelligent curiosity thing down pat.
What I feel about this election is simple. I'm sad that my country-people are so ignorant. And I'm scared that there are more of them than there are of us and President Trump is in our future.