We describe the electoral history of one of Europe’s most successful party families over the past 100 years in 31 countries. With a unique and newly collected dataset of national election results and a large number of economic and social variables measured for each country-election observation, we find that two main factors drive the electoral performance of social democratic parties: public-sector spending and the size of the manufacturing sector. Our findings suggest that most of the fall in support for social democratic parties in recent years is correlated with a decline in the number of industrial workers as well as a reduction in the propensity of social democratic parties’ core supporters (industrial workers and public-sector employees) to vote for them.

This letter investigates how voter transitions between parties affect parties’ policy positioning. While a growing literature investigates the role of election results as signals for parties’ policy adaption, it has mostly focused on vote changes of individual parties. However, parties do not know only whether they have won or lost in an election; they also have detailed information on which parties they won votes from and which parties they lost votes to. We make two arguments about how voter transitions should affect the strategic policy choices of political parties. First, when a party has lost votes to another party it will adapt its policy positions toward that party. Second, parties that have overall lost more votes become more likely to adapt their positions. Making use of a data set on individual voter transitions and party positions we can demonstrate that voter transitions indeed affect parties’ competitive behavior.