What Untermensche said.
There are objective and concrete reasons we can point to for hating Bush/Cheney (e.g. war and recession).
Why did conservatives hate Obama so much? There's a difference between legitimate disagreements with policy and the irrational fear vomited forth from conservatives regarding Obama.
What was also revealed was the rotting framework of American culture. I knew racism still existed, but to me it seemed a thing slowly but surely fading. Good god was I naive, and therefore wrong as wrong could be. I'm still dumbstruck over it. Anyway, I'd guess that's where at least a plurality, if not a majority of the hate for Obama came from. Second in line is Fox, Limbaugh, etc. ... Hmm. I think it's quite possible that conservative allowed the racism to remain flash-frozen until a demagogue like Trump came along to heat it to a boil.
All I know is that we're fucked.