This article aimed to explain conservative social movement's infiltration into and capture of the Republican party by utilizing the concept of 'movementization of the Republican party. In line with this purpose, this article conceptually differentiated social movement and political party, explained why European-style movement parties have rarely been observed in the American political soil, and reexamined the heavy impact of social movement on political parties on the basis of movementization of political party, with the Republican party in mind. Regarding the factors affecting the movementization of the Republican party, this article emphasized 'party hollowing as a general factor applicable to both Democratic and Republican parties, and the activation of para-parties and the ideological and identitarian consolidation of conservative voters, specifically for the Republican party. Finally, this article analyzed the movementization of the Republican party by relying upon such concepts as infiltration and capture, and by applying those concepts to the cases of the Tea Party and MAGA movements.