After more than four decades of immunity to the extreme-right party family, this Portuguese exceptionalism came to an end after the electoral breakthrough of the Chega party in the 2019 general elections. Drawing on a case study approach, this article discusses different explanations for the timing of Chega’s emergence in Portuguese mainstream politics in the late 2010s. Considering this late success, Portugal can be seen as a crucial case study to assess the available theories. This investigation employs a popular schema that implies the distinction between explanations focused on ‘demand-side’ factors (the protest voting thesis and the public salience of immigration) from those concerned with ‘supply-side’ factors (the spatial competition theory and internal supply factors). Through the employment of the congruence method, this article highlights the interaction between party-centric factors as a more appropriate explanation for understanding the timing of Chega’s electoral breakthrough than demand-side approaches.