In the lead-up to the 2005 federal election, as a reaction to Schröder's Agenda 2010 reforms, Lafontaine joined the newly-founded left-wing party Labour and Social Justice – The Electoral Alternative. Following a merger with the Party of Democratic Socialism in June 2007, he became co-chairman of The Left. He was the lead candidate for the Saarland branch of the party in the 2009 Saarland state election where it won over 20% of the vote. He announced his resignation from all federal political functions after being diagnosed with prostate cancer in 2009. He retained his position as a member of the Saarland legislature, and since May 2012 has been leader of the opposition in Saarland.