However , several well-known members of the Party , including Laurent Fabius , and left-wingers Henri Emmanuelli and Jean-Luc MÃ lenchon , asked the voters to vote `` no '' in the 29 May 2005 French referendum on the European Constitution , at which the proposed Constitution was rejected . However , several well-known members of the Party , including Laurent Fabius , and left-wingers Henri Emmanuelli and Jean-Luc MÃ lenchon , asked the public for a `` no '' vote in 29 May 2005 French referendum on the European Constitution , where the proposed Constitution was rejected .