For a more substantive analysis, I don't think there is one definitive source. I'm not sure which sources to start with, really. So it's more about a general research and watching, reading many different sources.
The explanation has something to do with the understanding that Americans do not feel represented by the American political establishment, understanding that the American political establishment and the military industrial complex are prioritizing the expansion of a kind of empire and/or influence around the world, at the expense of the citizens who pay taxes. Americans pay hundreds of billions to influence the world, but large cities are falling apart with crime, homelessness, etc.
Trump comes into the picture because he is challenging this status quo... he is not doing so in a traditional political way... because that "game" is already rigged. If you don't hack into the political game, no candidate outside of "the machine" will ever win. Trump achieved hacking this machine by being a kind of political "character" and out-playing the establishment's tactics, however the cost of doing this is that many people who don't understand this will see it as disrespectful and harmful to politics. Then his policies reflect a moderate stance that at the very least slows down the aggressive expansion of the "empire", while attempting to fix a few things at home.
That's a lot, but it doesn't even scratch the surface. I suspect this is part of the reason there are information bubbles. There is so much information that cannot really be disseminated efficiently. It's hard to talk about this and so it's hard to come to a wider consensus.