Social democratic parties are crumbling at the polls. Surprisingly, however, the causes of this demise remain largely unexplored. This article contributes to filling this gap in the research by studying the long-term impact of welfare state generosity on the vote share of social democratic parties in 16 Western European democracies. If the welfare state indeed was a key factor behind social democratic growth in the past, we ask whether the recent plight of these parties is down to a reversal of their previously dominant success factor? The article makes three principal findings. First, we show that social democratic parties primarily benefited electorally from expansive reforms at lower levels of welfare state generosity. Second, we find that this dynamic of diminishing returns also helps explain the demise of the Social Democratic party family in the whole of Western Europe. Lastly, our results reveal that programmatic turns to the right predict electoral losses in the least generous welfare states, whereas such shifts either pass unnoticed or predict vote gains in the most generous ones. We conclude by arguing that the structure of welfare state institutions is one important explanation for variations in the demise of the once powerful Social Democratic party family.