In 2007, Lang agreed to become co-chairman of a commission drafting changes to the Constitution that were supported by President Nicolas Sarkozy but opposed by the Socialist Party. This decision provoked strong criticism from his party, leading him to end his role in the party leadership. When Parliament voted on the constitutional changes on 21 July 2008, he voted in favour, becoming the only Socialist deputy so to do. A three-fifths majority was required, and the changes passed by a vote of 539 to 357, meaning that Lang's support enabled the bill to pass by a one-vote margin. The Socialist Party denounced Lang for this vote; party spokesman Julien Dray said that he had "gone too far" and "no longer has his place in our political family", while Jean-Marc Ayrault, the President of the Socialist Parliamentary Group, said that Lang's vote was an act of "crossing the Rubicon". Lang replied by saying that it "is in nobody's power to strike me from the map of the French political landscape".