Actually it was both. Have you not been paying attention to the backlash that Obama had by his former supporters during his second term?! I know I did.
Underestimating White people's anger got people comfortable in 2016. Nobody should make that same mistake again.
Why do you think people believe Biden would have beaten Trump in 2016 when he's more closely tied to Obama than Hillary is? It's because Obama was not viewed as the problem in 2016. Have you seen Obama's approval rating? Since it crossed
50% in late July/August 2016 it has been steadily rising. Again, associating with Obama, a popular former POTUS, isn't going to hurt Biden or any other Democrat in the states that are in play.
Nobody is underestimating white people's willingness to destroy the country; however, it's laughable to discount 2018 and pretend that 2020 is going to have the same conditions as 2016.