The Party of Social Democracy (Spanish: Partido de la Democracia Social, or PDS) is a Chilean social democratic party that was founded in 1972 as the political arm of the anti-Communist left. As such, it is often described as a center-left party as few of its members were Communists and many of them were in fact exiled during the two decades of Communist rule. In 1990, the party ran its own candidate, before forming the People's Democratic Unity with the Democratic People's Socialist Party prior to the 1994 elections to unite the left. This measure was successful when the UDP won control of both Congress and the Presidency in 1998 behind Ricardo Lagos. The PDS was frustrated in 2002, however, when the PSDP backed the more radical Isabel Allende for President over PDS candidate Enrique Borrero or moderate PSDP member Michelle Bachelet. In 2005, the PDS staged a walkout at the coalition convention when Bachelet agreed to allow the Communists into the coalition in return for campaign support, mobilizing the right and dividing the left. The PDS candidate in 2006 and 2010 was Borrero, and the PDS won the most seats of any non-coalition party in the 2010 elections, becoming the main opposition part to the CDN.