Organized labor is one of the largest voluntary organizations in the United States, representing over 14 million members in a sophisticated network of local, state and national unions interconnected through labor councils, state organizations, and national federations that mount significant electoral and lobbying campaigns. Despite these apparent strengths, organized labor has suffered numerous setbacks including the continued failure to pass national labor law reform and the retrenchment of public sector collective bargaining rights in Wisconsin, which suggest they are less politically effective than we would expect given their membership and resources. Why does organized labor punch below its weight in American politics? This project emphasizes the important role of institutions-namely divided labor law and federalism-in shaping the composition, size, strength and effectiveness of organized labor in the American politics. Exclusion of public sector employees from the foundation of private sector labor law, the Wagner Act, or their own comparable national level law, firmly situated private sector law at the national level while relegating public sector employees' efforts to gain collective bargaining rights to the state and local level. The national vs. state and local level as sites of demand making are not equivalent. Unable to ride on the coattails of private sector union growth at the national level, public sector employees' had to fight for legal recognition in every state and locality. Public sector employees' efforts progressed slowly, were limited to union friendly states, and the collective bargaining rights they did obtain were highly unequal and vulnerable to retrenchment. iii As a consequence of divided labor law, public and private sector unions peaked at different times, preventing a large public/private union movement. Further, divided labor law has contributed to public sector union members' continued legal vulnerability, the current geographic concentration of labor, and lasting divisions within organized labor that affect union members and leaders' political behavior today. Divided labor law thus fundamentally altered the development of organized labor over the last half-century in the United States, shedding light on the labor movement's weak political punch despite the strength and depth of its membership and resources. This work illustrates the powerful role institutions can have in shaping the fortunes of a seemingly "private" organization and, further, sheds light on the current battles over public sector collective bargaining rights in states like Wisconsin. iv