IN March 1964, President Lyndon B. Johnson eyed one of the toughest unfinished tasks he had inherited from John F. Kennedy: creation of a national health care program for the elderly. With typical ambition and determination, he told his aide on health care, Wilbur Cohen, "We're going to spend the rest of our lives if necessary passing medical care." Fifteen months later, on July 30, 1965, Johnson traveled to Independence, Mo., and with Harry Truman at his side, signed the legislation that created Medicare, whose 40th anniversary we celebrate today.