This panel is the beginning of a dialog on building a Left Opposition in the United States during the Trump era. It is an attempt to avoid repeating the mistakes of the anti-Bush opposition of last decade. We are the beginnings of a left socialist faction within the Green Party US that believes independent, class-based politics within a broad and expanding party. Our goal is to provide a platform that can unite the Left across parties and help to build a genuinely mass anti-war, anti-capitalist movement regardless of political party and affiliation. As such the panelists will outline, discuss platform building, and engage in a broader cross-Left conversation.