Among the many consequential political changes exposed and amplified by the Trump phenomenon have been the revolutionary developments in the character of the Republican Party. In this chapter, we conceptually profile the GOP’s illiberal, populist turn from more classical liberal understandings of conservatism. We then trace the roots of this movement from early antecedents through the Tea Party and Trump eras, and revisit the implications of illiberalism and populism for congressional politics and policymaking. Finally, we consider the illiberal and populist political strategies of Republican congressional candidates in the 2024 election. While much of the revolution is rhetorical, at least for now, we argue that major conduits of contemporary campaign communication, especially social media, combined with a configuration of institutions that amplify and entrench the most zealous evangelists for this new style of politics, indicate that this Republican revolution is unlikely to be rolled back. The illiberal, populist makeover of the GOP may endure as a cornerstone of Trump’s political legacy.