Trump succeeded because he went against the conventional wisdom in a way that resonated with what some people were deeply fed up with.
To take just one example, for years every Republican candidate trotted out the line of "Islam is not the enemy of the United States, but radicalism and terrorism is, and it can never be tolerated (even if we have to violate the rights of Muslims sometimes)", which people by and large could agree with but also looked at the continuing incidents of terrorism as smell as being bullshit.
Now Trump comes along with "Islam is a terrorist religion and I'll keep them all out of our country". It's a strong position to take, one that any conventional politician would take as inviting accusations of bigotry, but Trump doesn't care about being seen as a bigot. He'll keep harping on the security angle until he can just frame Muslims as not deserving of immigration or privacy rights because they breed terrorists.
It's not good logic, but it does have a certain appeal from the perspective of people who have listened to politicians trying to juggle the Terrorist Threat and Must Not Be Bigoted balls at the same time for the past 15 years. And he doesn't just do it with that, he does it with every issue he can. He eats Taco Bell on Cinco De Mayo and posts it on Twitter while calling illegal immigrants violent felons. This level of unflappable not giving a fuck and homing in on what parts of the typical message really are bullshit has a way to turn every accusation, both legitimate and illegitimate, against its source.
And now, if that wasn't bad enough, this guy is being pitted against Hilary "Rod Ham" Clinton, who is made entirely of bullshit and has no form but appeasement. She doesn't just play politics, anybody can listen to her for five minutes and know that she traded her flesh and blood for constituent polls and stump speeches years ago. She is literally everything Trump's supporters are raving about and her opponents hate in principle whether they support Trump as a result or not. Bill set up this era of party politics and she's its paragon, to the point that we have the DNC secretly calling the election for her on the day the primaries started and her only primary opponents being some dweeb and a guy who isn't a Democrat. And the dweeb was less popular than him by an order of magnitude!
This election isn't the showdown between liberals and conservatives, or between business as usual and revolutionary change. It's literally the showdown between the lies we tell ourselves and the lies we tell each other. Nobody is coming out of this election satisfied, and crazy though it may seem to say in the face of Trumpmania, I'm not convinced that 2020 won't be even worse unless Trump or Clinton somehow manage to give the country catharsis.
Fuck it, I'm voting for Johnson.