This Sandernista third-party idea isn’t going to work. It will be torn apart by SJW fruitbats. An economic-populist/progressive party like these folks are advocating would be fighting a three-front war against the neoliberal center, Trumpian right, and SJW left.
If these folks think the neoliberals worked overtime to screw them over when they were working inside the Democratic Party, they will be in for a rude awakening when they see how they are treated when they try to work outside the two-party system. The Democrats and Republicans will collude to throw up every possible obstacle to ballot access, and the courts will rubber-stamp such efforts. The full range of the media, from MSNBC to FOX, will try to ignore them. If that doesn’t work, they will vacillate between denouncing them, trying to create division among the third party’s supporters, and trying to co-opt them. Look at how the neoliberals have treated figures like Ralph Nader, Jill Stein, and Tulsi Gabbard. The Sandernista Party will be under such attacks from the neoliberal establishment, while being denounced as commies by the right and consumed by the SJW cancer within their own ranks.