Democracy is hard work. It can flourish only when citizens actively participate in the business of collective self-government. Yet political participation gives rise to deep political divides over core political values. In the midst of these divisions, citizens are required to recognize one another as political equals, as fellow participants who are entitled to an equal share of political power. Research shows that political engagement exposes citizens to forces that erode their capacities to regard their political opponents as their equals. In the course of democratic participation, we come to see our opponents as inept and ill-motivated, ultimately unfit for democracy. This tendency is especially pronounced among those who are the most politically active. Democratic citizenship thus can undermine itself. With this conflict at the heart of democratic citizenship, we must actively pursue justice while also treating those who embrace injustice as our equals. Sustaining Democracy navigates this conflict. It begins by exploring partisanship and polarization, the two mechanisms by which citizens come to regard their opponents as unsuited for democracy. It then proposes strategies by which citizens can mitigate these forces without dampening their political commitments. As it turns out, the same forces that lead us to scorn our opponents can also undermine and fracture our political alliances. If we are concerned to further justice, we need to uphold civil relations with our opponents, even when we despise their political views. If we want to preserve our political friendships, we must sustain democracy with our foes.