When people keep telling you to grow up you might consider the possibility of growing up. You hammered every alternative to Bernie as hard as you could and then his voters failed to show up. Net result, some degree of damage to every other alternative to Trump, the existential threat, all in service of a pipe dream. Politics is an adult pastime with tough real world consequences for everybody, and Biden is no where near as bad as you paint him. Biden will go just as far for progressive issues as his voters will allow/support. I might add that according to the Kaiser Family foundation, a majority of Voters oppose Medicare for all if it means eliminating private insurance or paying more in taxes, both of which are called for in Sanders' plan.