This dissertation offers an analysis of the New Politics movement to reform and realign the Democratic Party in the late 1960s and early 1970s. The central problem is to develop an understanding of the origins, nature, and limits of the reform movement. This study also addresses questions regarding the interactive relationships between political parties and social movements, the capacity of social movement actors to transform party institutions to better influence American public policy, and the role of contingency and agency in moments of political crisis. Whereas many scholars have interpreted the New Politics movement as a conflict between amateurs and professionals or blue collar workers and white collar reformers, I offer an explanation that roots the New Politics reform project in the longer historical struggle over Democratic Party structure and programmatic identity going back to the early New Deal period. By placing the New Politics movement in its proper historical and institutional context, this dissertation draws on extensive archival research as well as participant interviews to reassess this episode of reform, not as an effort to dismantle the party but to renew it by transforming it into a party of a different type. This study finds that the New Politics movement, while scoring many important victories, such as including more women, young people, and people of color in the party hierarchy, failed in its ultimate ambition to build a national programmatic party due to the staunch opposition of state party leaders, cold war intellectuals, and especially the leadership of the trade union federation. This was due primarily to the labor movements own institutional position in the party, which channeled its influence through the smoke-filled back rooms of elite brokerage an arrangement which democratizing the party threatened. Rethinking the New Politics movement challenges the predominant narrative that treats the post-1980 reorientation of the Democratic Party toward the political center as the inevitable and common sense response to the excesses of the late 1960s. As I try to show, rather than the inexorable result of liberalisms failures, the making of the modern Democratic Party was the result of a struggle between contending political projects. While the New Politics did not succeed in winning that war, it did decisively shape the contours of Democratic Party politics today.