A lot of the blame lies with hugely popular but horrifically evil conservative commentators, for example Rush Limbaugh.  Some of his quotes:

On sexual consent:
"How many of you guys . . . have learned that 'no' means 'yes' if you know how to spot it?” 
On climate change:
"just a bunch of scientists organized around a political proposition."
On feminism:
 "was established so as to allow unattractive women easier access to the mainstream of society."
On Obama:
"I hope he fails."
On Ebola:
 "People at the highest levels of our government say 'Why, why shouldn't we get it? Why should only those three nations in Africa get it? We're no better than they are.' And they have this attitude, 'Well, if they have it in Africa, by God, we deserve to get it, because they're in Africa because of us and because of slavery.'"
On Sport:
"the NFL all too often looks like a game between the Bloods and the Crips without any weapons."
On drugs:
Defended mandatory minimum sentencing for drug offenses- was later investigated for illegally obtaining the prescription drugs oxycodone and hydrocodone and admitted his addiction.
A familiar example for Trump to follow:
Claimed Michael J Fox was shamelessly acting - and mocked him on camera - when Fox was campaigning for Parkinsons sufferers
On tobacco:
"Smokers aren’t killing anybody"

And it looks like only one of those things has come back to really bite him, probably terminally.