Although it's still a bit early, I think the Democrats are gonna get washed in 2018 and 2020 (barring the emergence of a savior-like candidate).
Warren doesn't have enough of a national profile and is too far left.
Booker's chance has passed, he's become more unpopular over time and he's been proven to have ties with Kushner and Trump.
Hillary's done.
Kaine is hopeless.
Harris is another DNC puppet who has yet to do anything of significance and has a shytload of baggage.
Gabbard is interesting but she may face heavy resistance from the establishment/party-line voters for not being liberal enough.
Biden's time has also passed; he'd be a sacrificial lamb for the DNC, if nothing else.
Bernie would be ideal if he were younger and if the democratic party wasn't so fractured; rightly or wrongly, many democrats blame him for the schism between the party establishment and its independent/swing voters.
Michelle Obama would probably be a better candidate than most of the aforementioned but her relative lack of experience, the country's current racial and political climate, and her lack of genuine interest in the position are holding her back. She'd be better-suited becoming a Senator and gaining some political experience before aiming for POTUS (if she ever wants to get into politics).
The party's a mess and is obviously still reeling from 2016. And it only has itself to blame.