This seems more of just a problem with how the two parties try to win by absorbing every fringe groups crazies cause into a national platform. It is a failing of our country to have hyper partisan politics controlled at a national level and holding all members in every state accountable to the same platform.
Naw my guy, the failures of the American left are rooted in its inability to be a party of the working class. Every lost election sees the policy of the Democrats moving further and further to the right, leading to a platform that masquerades as progressive but actually alienates and abandons working class Americans because it isn't actually committed to them. Bernie was the first step (although many argue he didn't go far enough), but since the us Democratic party is held by the same corporate reins as the Republican party, he wasn't given a fair chance. If you look at other developed countries, even America with its most blue government is still to the right of center on economics.