Can socialism, in whatever form, gain political traction in the United States without revolution?
I have little doubt that a new, more or less socialist left, can happen here (and already is slowly emerging). The reason is simple: socialism was born with capitalism, is its shadow/other, and is provoked and revived by capitalism's own mechanisms (e.g. crises like this one). Those who suffer, like those able to see and sympathize with the suffering, caused by the deep irrationality of capitalism (e.g. imposing austerity on a recessionary economy, enlarging the homeless population alongside the empty homes, deepening the wealth and income inequalities that helped to cause the crisis during the crisis, etc.) will sooner or later rise from a focus on fixing the system to fundamentally changing it. At that point - unique in each culture and indeed in each individual - the rediscovery of the rich accumulated theoretical and practical tradition of socialism resumes. Marx and Marxism are rediscovered, etc.
I don't know if what results will use the name socialism or some other(s), but it will in any case be a new and unique outgrowth of an extension from socialism. And part of its differences from traditional socialism will emerge from flaws and critiques of the earlier experiments (Soviet, Chinese, etc) that will clear the way.
Anyway, that is how the situation seems to me as I do both public speaking and media work and encounter the profound shifting already underway in the consciousness of so many in the US.