“A delegation of former Lyndon Johnson aides, led by Bill Moyers and Jack Valenti, demanded yesterday that the History Channel launch an independent investigation of its documentary charging that LBJ was involved in the assassination of President Kennedy.” The network has agreed to review the issue internally, but isn’t specifying how far it intends to go in complying with the Johnson staffers’ demands. Initially, the network had defended its airing of the documentary as a legitimate expression of an unpopular point of view, but that defense is faltering as those close to Johnson offer evidence that directly contradicts that allegations made in the film.