For years, academics, political theorists, and campaign finance reformers have debated the causal relationship between campaign contribution limits and the outcome of elections. Some argue that limiting campaign contributions amounts to "incumbent protection;" others contend that limits make challengers more competitive. This study is the first of its kind to comprehensively examine the states with contribution limits and empirically measure changes in competitiveness. Based on an analysis of 30,000 elections in 45 states, this study found that campaign contribution limits slightly favor challengers by reducing the incumbent margin of victory.