This article investigates how established political parties react to the emergence of a far-right party. Prevailing approaches explain established parties’ reactions either as based on a spatial model of politics or as determined by historical trajectory and political culture. Neither approach sufficiently accounts for how party leaders choose between these competing motives for actions or how their strategizing might evolve over time. To complement existing approaches, I suggest understanding the emergence of far-right parties as a problem of interpretation. How parties react to far-right emergence depends on what kinds of heuristics they draw on to make sense of the phenomenon of far-right voting. To validate my approach, I study different stances Germany’s center-right Christlich Demokratische Union Deutschlands (CDU) has taken toward two far-right parties in postwar West German history: the Nationaldemokratische Partei Deutschlands (NPD), from 1964 to 1969, and the Die Republikaner (REP) from 1983 to 1990. Using archival material documenting internal deliberation, I argue that the social sciences have played a crucial role for how CDU leaders have evolved in their interpretation of far-right emergence. In the 1960s, party leaders drew from external social expertise on the far-right to discount the idea that the NPD was a resurgence of Nazism. In the 1980s, they were concerned with a reform project of their own party, leading them to grasp the REP through heuristics provided by scholarship on electoral strategizing. This resulted in a shift in strategies of repression against the NPD to strategies of demarcation versus co-optation against the REP.