The study of regime diffusion tends to focus on external diffusion effects that support democratic change and consolidation (Di Palma 1990; Huntington 1991; Pevehouse 2002 Levitsky and Way 2005; Brinks and Coopedge 2006). This paper brings to light regime diffusion effects that help reinforce the authoritarian political status quo. Specifically, it examines the effect of the Iraq War on opposition cohesion in Arab countries and on regime survival tactics. Using process-tracing evidence from the cases of Egypt and Bahrain, the paper highlights the contradictory impacts that the Iraq War had on the processes of political reform in the Arab world. On the one hand, the political ascendance of self-proclaimed Shi'a political groups in Iraq encouraged Shi'a opposition groups in the other countries to mobilize in demand greater political rights. On the other hand, sectarianism in the new Iraq helped crystallize sectarian differences among the opposition, and allowed regimes and their supporters to exploit these divisions to undermine the legitimacy of Shi'a political demands. Indeed, joint concerns over the US invasion of Iraq provided ideologically diverse political groups with a rare opportunity to work together to coordinate their opposition to their regimes' tacit support to the war. At the same time, evidence indicates that incumbent regimes were relatively successful in undermining the credibility of their oppositions by capitalizing on public discontent with US policies in Iraq and on the apparent overlap between the demands of their opposition and US-led democracy promotion efforts. Based on this evidence, the paper argues that the study of Arab authoritarian durability must award greater attention to the impact that troubled political transitions have had on processes of political reform in Arab countries. It also calls for a more systematic study of the opportunities and costs of cross-ideological opposition mobilization strategies that invoke Pan-Arab causes, such as Iraq and the Arab-Israeli conflict. A richer understanding of how these issues have impacted political reform efforts in the past may offer some useful clues about the origins of authoritarian durability in the Arab region.