I think there are three elements of the Democratic thinking which are ‘doomed’.
1. Hillary Clinton ran with a fantastic amount of money and an arsenal of strategists. She could not convince the general public outside of metropolitan areas that she had any theme or message that concerned them. The 2020 group of candidates would have to go and convince people that they have their best interests at heart.
2. The economy is moving along like a 1964 Cadillac Eldorado. Smooth ride...jobs opening every week...tax revenue being created for the federal and state coffers...low unemployment.
3. Based on ‘chatter’, I’d say that Donald Trump in 2020 will double his black and Latino vote count (in some states, maybe even triple what he got in 2016). If this shapes up, it’s a major problem to gain those votes back in future elections.
The thirty states that Trump took in 2016? Pretty safe, and he’ll likely add two or three additional states.
WI seems unlikely in 2020.