Following the
May 1947 crisis, during which
Maurice Thorez (Communist vice-premier) and four other PCF ministers left
Paul Ramadier's government, the UDSR took part in the
Third Force coalition which united centre-left and centre-right parties in opposition to the
PCF on the one hand, and the
RPF on the other. It remained, throughout the Fourth Republic, a minor centrist political party, though it participated in various governments. Its president
René Pleven was named
President of the Council of Ministers from 1951 to 1952, before being succeeded by
Antoine Pinay of the
CNIP. Pleven's leadership was eventually challenged by
François Mitterrand, who advocated a realignment to the Left, and took the lead in 1953. In 1956 the UDSR participated in the centre-left
Republican Front coalition, headed by
Pierre Mendès-France, which won the legislative election. However, two years later, the UDSR imploded; indeed, Pleven and the party’s conservative wing approved
Charles de Gaulle's comeback during the
May 1958 crisis, in the midst of the
Algerian War and threats of a coup d'état, and the institutions of the
Fifth Republic, unlike Mitterrand, who called the
new Constitution a "permanent coup d'état." == Legacy ==