Turning to the personal, in recent days I have spoken to three individuals (2 of whom are very close to me) who have told me that if Biden is the nominee they won't vote. That concerns me.
I think there are two sides to the "electability" debate. On one side the assumption that one needs to be white and male to be elected to our highest office is problematic. On the other it is undeniably true that if Hillary Clinton was a man she would be our President right now.
The unmitigated disaster that would be another four years of our country being run by an incompetent and corrupt Putin puppet has people nervous. Rightfully. But I don't think that means we need to shy away from a candidate that would excite the electorate to vote for him/her, as opposed to it being primarily a vote against Trump. And you pinpoint why.
Plus, if the economy was on an upward trajectory I would say that despite historically low approval ratings Trump is a threat to win in 2020. Unfortunately I don't see the economic outlook a year from now being better than it is now. A candidate with a 42% approval who needed 46% to squeak out a victory against a candidate who was, frankly, not that great a campaigner...if that holds the "electability" of the Democratic candidate will not be a factor.