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.