Make no mistake about it, I will support whomever runs against Trump. If you remember, even 2016, I said we needed a new, younger generation to be running.
The only chance Bernie would have to win is if the DNC and all the progressive PACs went beyond scorched Earth against Trump which I find highly unlikely. Dems have not done that nationally in my lifetime and it has cost the nation dearly. Trump and his minions will spend well over a billion dollars tarring Bernie as a Socialist/Communist and worse. If he and the Dems don't fight that fire with nukes, he will lose big and Moscow Mitch will get more power.
Whether you are handicapping a horse race, a bball game or a political race, you have to look at past performances. The Dems have never been willing to deeply attack. Even if those attacks are telling 100% truth. They would have to do that with Bernie or Warren as the nominee.
I wish there was a 45-50 yo progressive candidate, but there isn't. The main two are too flawed to beat Trump. I wish it was otherwise, but it isn't.
P.S. If you actually paid attention to what the core of what I post about millennials, you'd see and admit that it is that you don't try hard enough and aren't willing to work with those who don't genuflect to your demands. If you can only get 80-90% of what you like you attack those who are mostly with you. Take it from us, just like we took things from our elders.
As importantly, don't be afraid to fail or get a bit bloodied (metaphorically). Make mistakes and learn from them. Don't take you ball and go home.