Just it being Hillary has a pretty big effect too, though. Many Republicans hate her with a burning passion and refuse to endorse her even when they say they won't vote for Trump.
The problem is that Trump is literally the worst candidate to ever win the nomination and his campaign is the worst GOP campaign ever. Literally every aspect about him has been deplorable and his campaign has basically no groundgame.
Which means that whatever results we see this November will literally be the absolute best results that are possible for Hillary. If that's only 2012 margins, then Hillary is fucked in 2020 so long as the GOP nominates someone even marginally better than Trump that year.
I am not at all convinced that Trump losing by an even worse landslide would cause a course-correction by the deplorables that put him on the national stage in the first place. The echo chamber they've built for themselves is just too strong.
If Trump were to lose by a double digit landslide, then the deplorables wouldn't openly admit it, but they would know deep down that the vast majority of people hate them.
Look at how people treat 2012 results. Sure you get someone occasionally bring up bullshit claims that Obama only won due to fraud, but the vast majority of people recognize that Obama won fair and square in that election, and NO ONE suggests that Obama only won in 2008 due to fraud.