It's a cult of personality. As to why they fixated on him, rather than some other rich bigot--well, how do you predict which video will go viral? It's a mysterious alchemy. Trump's mix of dumbing his speech down to act like his idea of "a rural high school educated person," his taking pride in being a dick, his willingness to blame all society's ills on minorities and women, his posing as an alpha male--all of this appealed to a group of people that make up around 40% of the Republican party and 20% of the overall electorate.
And now that it is a cult of personality, there is literally nothing that can dissuade them from supporting him. What's right is now defined, in their mind, by what he does. They get all their news from him, since he's told them the rest of the media is giving them fake news. He can be as corrupt as he wants because when he says he did nothing wrong, that's what his base hears.
Fortunately, his base is a minority of the nation. So this isn't quite as dangerous as a personality cult leader who has the majority of the nation behind him.