Repub leaders have fanned the flames of bigotry & fear for decades, just a lot more quietly than Trump. At the same time they've enabled the looting of the economy & blamed de gubmint for what their free market ideology has accomplished. The cognitive dissonance that causes in their followers is huge. They can only compartmentalize just so much before they reconsider or burst out in fits of rage & frustration. That's what Trump has brought out, a great venting of conservative angst. They know they're getting screwed. They don't know that what they believe in is what's screwing them.
The people at the top of Republicanism got arrogant & complacent, thought they could control these poor propagandized people forever w/o delivering on anything. And why not? It worked for 30 years. That was until Trump saw it for what it is, an opportunity for demagoguery, believers desperately seeking leadership, seeking someone to believe in. The base has been primed & ready for a long time, yearning to hear what Trump knows they want to hear so he gives it to them.
I hope you don't think that Donald believes a word of it, because he doesn't. It's all weaponized insincerity.