In this paper we investigate the programmatic determinants of support for social democratic parties in Western Europe. Social democratic parties have seen a strong electoral decline in the past 20 years. This development has been linked to the structural transformations of post-industrial societies and the programmatic choices of social democratic parties in a transforming political space. While much debate exists about how specific strategic choices of social democratic parties have affected their support, empirical research on this question is scarce. The observational studies that do exist face the fundamental challenge that party positions (for example measured through manifestos) and electoral performance are likely endogenous. In order to address this issue, we have fielded conjoint experiments in 5 Western European countries (AT, DE, DK, ES, SE) in which respondents can choose between social democratic programs that vary on a number of issue dimensions. The findings allow us to show the potentials of different programmatic appeals to different societal groups. They indicate that social democratic parties indeed face a fundamental trade-off when it comes to their positional choices. These findings provide an important contribution not only to the study of social democratic decline but also to questions of representation in a changing political space more generally.