The chapter summarizes the New Progressive Dilemma (NPD) debate, identifying three arguments from comparative welfare state and party research likely to be relevant to the relationship between immigration and welfare state retrenchment: public opinion, welfare institutions, and political parties. Alignment of anti-immigrant sentiments and welfare support varies considerably between countries, especially between the US and Europe, leading to different party incentives vis-à-vis welfare state retrenchment. The chapter introduces insights from comparative welfare state and party research to the debate, discussing inter alia, political parties in terms of welfare retrenchment, immigrants as a voter group, and cross-national variation of existing welfare institutions. It addresses the complex debates around attitudinal change caused by immigration, levels of welfare support, voting behavior, and social expenditures. Combining these strands of literature, a common theoretical framework is developed that is subsequently applied to both the US and Western European context.