In 1959, the Swedish Social Democratic Party prevailed over the bourgeois parties in the great battle for supplementary pensions (ATP). In the 1990’s, however, the party leadership decided to abolish the ATP in close cooperation with the bourgeois parties. The thesis poses the following question: “What prospects did the Social Democratic leadership have to gain support for the ATP-reform in the 1950’s, and then for the quite dissimilar pension reform in the 1990’s, and how can differences between these prospects be explained?” In order to explain the kind of party change pointed out in the problem statement, this thesis proposes a theoretical perspective that focuses on the tension between different roles played by the party leadership on different arenas. The hypothesis, that is tested in the thesis, is that early decisions create different constrains for future decisions on different arenas. The thesis has two main conclusions. The first conclusion is that the decision to implement the generous ATP-system in the 1950’s in practice laid the ground for the subsequent abolishment of that same system in the 1990’s. The second conclusion is that the pragmatism, always displayed on the parliamentary arena, has not been visible on the electoral arena or on the party arena. The party leadership plays different roles on different arenas, and over time these different roles have become hard, if not impossible, to combine. The result of this was that decisions on the parliamentary arena were decoupled from messages and rhetoric about these decisions on the party arena, and on the electoral arena. The pension reform in the 1990’s was quite a different decision compared to the popular introduction of the ATP-system. Both of these decisions, however, were attempts by the party leadership to maximize support on each arena. The possibilities for succeeding in this venture were greatly reduced in the 1990’s. Instead of one party striving for one goal, Swedish Social Democracy in the 1990’s appeared as two or three parties, with different objectives and goals.