Another thing is a lot of people that were supporting. Bernie Sanders only started engaging in politics because of Bernie Sanders. I knew lifelong green party people who boycotted the Democratic Party who registered as Democrat for the first time in their lives to vote for sanders.
Believe it or not, there are quite a few socialists in the United States. And essentially, those guys with the anarchist T-shirts were willing to vote for sanders, but not a mainstream Democrat. Plus, making a few campaigns stops in Wisconsin would’ve helped Hillary a great deal.