This article focuses on the joint campaign of “remigrés” and American authorities to “westernize” the local Social Democratic Party (SPD) in Berlin during the early Cold War. The years 1948 to 1958 witnessed one of postwar Germany's most bitter intraparty struggles for leadership within the Berlin SPD, where a faction of remigrés led by Ernst Reuter and Willy Brandt wrestled for control with the so-called Keulenriege around Franz Neumann. Examining clandestine American support for the remigré faction, which included favorable media coverage and considerable financial contributions, this article focuses in particular on the political maneuvering of a German-American network around Shepard Stone, political advisor to U.S. Commissioner John McCloy. An investigation of the postwar power struggle within the Berlin SPD offers fresh perspectives on three related subjects: the role of remigrés in postwar Germany history; the political clout of informal German-American networks; and West Berlin as an alternative laboratory of German democratization.