Party identification (PID) is a central concept for the explanation and prediction not only of electoral choices but also of issue attitudes and political perception. The traditional conception of PID attributes its formation mostly to citizens' primary socialisation by family and primary social groups. While it has often been debated in the literature whether PID really is an "unmoved mover" or subject to feedback effects from the political performance of party candidates or their issue positions, this discussion has usually focussed on the national level. We complement this perspective in two ways: first, by looking at feedback effects that originate at the level of individual US states, second, by looking at the socialisation effects of the partisanship of presidents and state governments. Using multilevel ordinal logit modelling applied to cumulated American Election Study data from 1958 to 1992, we show that even after controlling for parental PID and other predictors, the party not only of the US president but also of the governor of the state experienced during adolescence and early adulthood affects the formation of PID. Our results confirm the importance of social identity theory for a complete understanding of citizens' partisanship.