MADISON, Wis. (AP) – A longtime top official with the state’s chamber of commerce is leaving his post to start a public relations firm.   James Buchen announced his departure Monday from Wisconsin Manufacturers and Commerce after working 26 years with the powerful lobbying group.  Buchen currently serves as senior vice president of government relations and will leave at the end of the year.  Buchen says his new firm will partner with Hamilton Consulting in Madison and provide a full range of public affairs services.  During his time at WMC, Buchen managed government relations, communications and public relations, litigation, political affairs and membership.