Republican discourses around immigration have undergone a fundamental shift in character over recent decades. Whereas GOP platforms initially embraced the Immigration and Nationality Act of 1965 and successive Republican presidents generally spoke in broadly inclusionist terms, saw little need for border fortifications, and then embraced calls for comprehensive immigration reform, strident opposition to the current immigration policy regime and backing for an impregnable border have now become contemporary Republican “commonsense”. Furthermore, very strongly restrictionist discourses, including some openly based upon race and ethnicity, have secured a place within the Party’s ranks. This chapter considers the reasons for this shift and argues that the original policy regime structured around the 1965 Act was weakly embedded within the conservative movement and amongst Republicans. Furthermore, over time, that regime was hit by sustained bursts of negative feedback as exogenous processes interacted with the endogenous sources of weakness. These interactions paved the way for the repudiation of the principles underpinning the 1965 Act, the side-lining of comprehensive reform plans within Republicanism and, as a corollary, a mainstreaming of restrictionist discourses. Nonetheless, while the 1965 policy regime has been abandoned across the right at both mass and elite level and there are promises of mass deportations, it does not as of yet command the resources or capacities necessary to usher in an alternative immigration regime.