sorry, but thats just not really true.
the democratic party has a very wide range of people and policies. on the far left of the party you find hardcore progressives, but they don't speak for the entire party. if you cast aside all of the moderate democrats in the party, you will NEVER win another national election again. this is what people miss with the "bernie would have won" talk. there are many moderate democrats that were turned off by bernie's rhetoric. talking about corporate interests and all of that is a largely meaningless discussion. money will NEVER leave politics. there is too much at stake, and lobbyists will continue to funnel money into the system from now until the time the earth becomes uninhabitable. some people are more beholden to their donors than others.
democrats lose elections because their voting base isn't mobilized and excited to get out and vote. obama, who you just criticized, was able to raise the energy and hope of the democratic base, but the turnout was limited to him, not downballot democrats. that was a big problem. the republican party is completely and totally fueled by a few large dynastic families in the united states. they run large companies and funnel in massive amounts of money into the republican system. republicans know if they go against the wishes of those donor networks, they will be primaried and likely voted out of office.
paul wellstone was one of my favorite politicians and was taken from this world way too young. but i also have a lot of respect for more moderate democrats too. "democrats" and "progressives" have most of the same policy goals and ambitions, and their views align much more closely than the views of, say, even the most moderate republicans.
i'll also not really stand for slandering of obama and what he accomplished. as soon as he took office, he faced a torrent of obstruction and racists attacks because he was the first black man ever elected president. i saw that up close and personal for 8 years here. his legacy cannot be evaluated without conceding that he faced issues and resistance that no other president ever faced. despite the incredible (and often unfair) opposition he faced, he lowered the uninsured rate and helped prevent the complete and total collapse of the US economy, and by extension, the world economy, which was a problem dumped on his plate before he actually even had a chance to breathe upon taking office.