Transportation public–private partnership (PPP) projects are long-term projects that usually break the status quo of public ownership. In fact, opposition to PPP projects stems from a variety of factors, such as political influence to favor certain interest groups and high toll prices. Close examination reveals that vulnerability to societal and political domains originates at certain individual points and creates a complex web of problems as it propagates through different socioeconomic and political levels and project stages. This article attempts to unveil such complex and problematic trends by analyzing ten failed transportation PPP projects to identify critical socioeconomic and political failure factors. Employing questionnaire surveys and path analysis, a failure-mechanism model is developed to depict all possible transportation PPP project vulnerabilities to the socioeconomic and political domains. This article's failure-mechanism model could act as a vulnerability-prediction model for transportation PPP practitioners in the public and private sectors, and it can help better understand socioeconomic and political issues’ impacts to transportation PPP projects.