This dissertation examines the relationship between grassroots progressive activists and the Democratic Party. Building on Hirschman’s (1970) framework of exit, voice, and loyalty, this dissertation combines literature on political parties, new media and politics, citizenship, and social movements to examine how progressive activists become activated in Democratic Party politics, how they negotiate their relationship with the Party, as well as the strategies and tactics they employ towards their political goals. To that end, I examined three pathways through which activists were attempting to influence the Democratic Party: as delegates to the 2016 and 2020 Democratic National Conventions, by involving themselves in and engaging in actions via the formal Party structure of the California Democratic Party, and by engaging in activism via local progressive groups. I explore these activist practices through a combination of direct observation, semi-structured interviews, social media analysis, and textual analysis. This dissertation explains how both the personal identity of activists as well as the collective identity of their activist groups influence how they understand the Democratic Party, what they think it can be, and how they conceive of their role in and around it. It also refines and extends Hirschman’s theory to both add the notion of “entry” and to show the hybridity of his concepts of exit, voice, and loyalty. I present numerous examples of activists entering Democratic Party politics in order to exercise their voices. Using the 2016 and 2020 Sanders delegations to the Democratic National Conventions, I argued that a self-reinforcing relationship exists between activists’ personal identities, the level of control exerted by a campaign, and the potential for the development of collective identity. In the context of internal party elections at the state level. I present the ideal opportunities, as well as the limitations of certain strategies and tactics for networked mobilization. In the context of local groups, I introduce two typologies—Party-First and Party-Second groups—for classifying and examining progressive activist groups based on the differences in both how they define progressivism and also the selection of and discourses surrounding the tactics they employ for political action. Beyond these theoretical contributions, this dissertation also provides a comprehensive understanding of what party activism looks like beyond participation in either candidate campaigns or delegations to national party conventions.