Rubio and Kasich are also completely nuts. The party has discredited all the institutions that inject reality into the discussion and so it has become completely unhinged, and it's all just a big affinity con. Republicans have long had tax cuts for the rich as a goal, but in the past, that had to be weighed against deficits and tough choices about what spending to cut. Now it's just, "we can cut taxes on the rich with no budget consequences and we don't even have to cut spending." So Trump can come in and just take it to 11.
"Oh Rubio wants to grow the military, not touch entitlements for anyone under 55, cut taxes by 700 billion a year and pass a balanced budget amendment? While, I want to cut taxes for the rich even more, protect entitlements for everyone and make the military even stronger!" Who can credibly tell idiot Republican voters that that's impossible? Not academics, not the media, not even the party (after all, they're backing Rubio's crazy shit).
And you have people like Atheist who don't even know anything at all about policy or real discussions, but respond to Trump's racism. Those guys used to just fall in line with the party, but they've been screwed enough to want something bigger.