Approximately one third of the world's states are competitive authoritarian regimes, where opposition parties compete against powerful incumbents that skew political and electoral institutions to their advantage. A key challenge for opposition parties in such regimes is to expand their electoral support and work with other opposition actors to win greater power. Under what conditions are they successful in building broad-based and coordinated challenges to authoritarian rulers? This dissertation argues that opposition success hinges on their strategic choices in elections and in office - and how they navigate key tradeoffs and dilemmas of expansion. Individual opposition parties face diverging incentives and costs to expand based on the identities and issues around which they initially build support. At the collective level, opposition parties often seek to coordinate their electoral challenges against the incumbent to build broader power. But when opposition parties work together, they face strong pressure to stick with their existing niche identities, since pursuing strategies of party broadening - changes to party image to appeal to new constituencies - risks encroaching on the electoral terrain and core constituencies of their coalition partners. As a result, parties frequently struggle to navigate conflicting incentives of individual and collective electoral strategies to win power. The dissertation tests the theory empirically using evidence from Malaysia, until 2018 the world's longest-running dominant party authoritarian government. It analyzes the strategies and variable success of the country's opposition parties in pursuing their core electoral and policy goals and coordinating their efforts in this environment - and why they were ultimately successful in securing substantial electoral support. Additional case studies illustrate how individual and collective dilemmas of expansion inform opposition behavior in other competitive authoritarian regimes. The study offers new insights into why opposition parties have difficulty in unseating even weak authoritarian incumbents, and the conditions under which they successfully scale up their power.