The Social Party of Colombia (Span: Partido Social de Colombia), often referred to by its acronym PS, is one of the main political parties in Colombia and is primarily the left-wing party since its founding in 1924. Its members often are referred to as Socialists in English or in Spanish, Los Sociales. The Social Party ruled post-Pacific War Colombia as a broad coalition party under the sixteen-year Presidency of Humberto Ruiz, often viewed as the moderate father of the party. Following his 1946 retirement, the party began moving gradually to the left under the Presidency of Rómulo Betancourt and more left-wing elements in Congress, both of whom were defeated in the 1950 landslide by the Christian Democrats. The Social Party moved away from the moderate social democratic Ruiz and Betancourt era to a more markedly socialist position by the 1960's, when Luis Beltrán Prieto controversially won the 1966 presidential election and sharply moved the PS to the left. This left-wing coalition was unsustainable and collapsed in 1970, leading to a return of somewhat more moderate leadership that returned Betancourt to power in 1974, although the left-wing insurgency fuming over the Brazilian War forced Betancourt to step aside in 1978 in favor of the more leftist Carlos Andrés Pérez. Pérez was subsequently ousted in the 1983 no-confidence vote after narrowly being reelected in 1982, with the PS barely holding a majority in the 1980 Congressional elections. The 1986 election was a disaster for the PS, throwing it into its smallest minority in history as moderate Socialists (known as Humbertistas) defected to the Republicans en masse. The leftist PS remained sidelined until the rise of Alvaro Uribe in the late 1990's, who moved the party back towards the center amid discontent with the governing Republicans, winning a strong electoral majority in the 2002 Presidential election and returning the Socialists to power in the 2004 Congressional election, although the PS would lose both the Presidency and both houses in Congress in 2010 due to public anger over Colombia's heavy debt and the PS's endorsement of liberal social issues at the 2010 party congress.