On April 1, 2000 he joined the Socialist Party and started to work at SP's think tank. Three years later he became director.
In 2003 he was elected into the Dutch Senate and was a member from June 10 that year till November 28, 2006. In November 2006 he was elected into the Dutch House of Representatives. The same month he changed positions, instead of being director he became SP's think tank chairman.