In the heat of the presidential campaign early this year, Jack Lang, a popular icon of the French left, accused Nicolas Sarkozy of “trickery at the highest level,” “anti-republican behavior” and — perhaps most cutting of all — being a “Bush adapted for France.” Now Mr. Lang, a former culture minister and education minister who served as campaign spokesman for the defeated Socialist candidate, Ségolène Royal, is the latest leading Socialist to defect to the Sarkozy camp. On Monday night, he announced that he was accepting President Sarkozy’s invitation to join his committee on modernizing France’s institutions. Threatened last week...