One of my frustrations with Ralph Nader was his absolute refusal to do anything about party building between presidential elections. He shows up as a spoiler vote every four years, but isn't really interested in the work required to make a structural change. Sadly, I see parallels with my fellow liberals and the Nader campaign. Effecting change takes a lot of work, and it takes constant work, even in off-election/midterm years. You can't pin your hope on some magical progressive pony like Elizabeth Warren or Bernie Sanders and think that suddenly everything will be rosy and liberal.
IT. DOESN'T. WORK. THAT. WAY.
Do you want to see liberals get more traction? YOU HAVE TO DO THE WORK. You have to show up to every election, so that politicians don't write you off as a neglible vote. You have to contact your elected officials and tell them you want progressive stances. You have to do this often and in large numbers to drown out the messages they're getting from the right. You have to contact media sources and demand that your side gets airtime. You have to complain when they do the bullshit "Both sides do it..."
You have to get involved in campaigns.
Look, that may sound like a lot of work--because it is--but that's EXACTLY what the right has been doing consistently for the last forty years. Liberals seem to think that the correctness of their beliefs (as proven over time) should give them gravitas, but facts are secondary to politics and media coverage. You need to be visible.
Until you're willing to do that, there's no way for Elizabeth Warren or Bernie Sanders or any other magical progressive pony to actually win an election.