Why go to the enormous (and almost guaranteed to be a failure) effort to start a third party when the Democratic party can be changed by people OWNING the label "Democrat" and doing the long-term political work to make this political label synonymous with the word "democrat"? White liberals want quick, easy answers to difficult political problems. Even moderate Democrats like Obama and Clinton could get quite a lot done for the middle class and the poor if the House were not so completely dominated by Republicans working in unison. Now is the moment, Republicans are divided like they haven't been in a long, long time. More liberal minded Americans have only one choice--unite behind the Democratic party warts and all. 
American women have long been aware of the fascistic and violent nature of an America dominated by Republican policies which is why they vote Democrat knowing full well it's the only option. Sanders would not be more effective than Clinton in this political climate.