This. I think both sides are underestimating just how much Hillary, specifically, was hated.
The GOP Slander Machine tries to turn every Democratic nominee into The Great Satan, but with Hillary it worked perfectly, for whatever reason. It was partly that they had more time for her: 25 years of constant screaming propaganda turned up to 11. But it was more that she actually was inherently unlikable and untrustworthy. She is a phony in ways that are keening and obvious.
We have nobody else like that. It doesn't mean we'll easily romp in 2020, but it does mean if we are smart we will get back a metric sh-t ton of people who voted against Hillary instead of merely for Dump or even against-any-Dem.