He did not accomplish that by himself. The entire Republican party is responsible for that. The megadonors, the evangelicals, Fox News, the NRA, Facebook and Cambridge Analytica, internet trolls, manosphere podcasters, all the way down to the lifelong down-ballot voters.
The Donald Trump that Trump voters see is not the same one you and I see, because theirs is nearly entirely fabricated from lies and omissions. They see fake successes and don't see real failures. Trump's benefactors, not Trump, constructed this alternate reality. And those voters have been living in this constructed reality for over a decade now, conditioned to protect it against all outside forces.
You're right, it's not just the idiocy of the country that put him there, but the evil of the conservative machine.