This episode's headline: Campaign '96; Political Wrap; Fight Against AIDS; The Mystery of Vermeer. ANCHOR: JIM LEHRER; GUESTS: MARK SHIELDS, Syndicated Columnist; PAUL GIGOT, Wall Street Journal; DR. PAUL VOLBERDING, AIDS Researcher; DR. JONATHAN ALLAN, AIDS Researcher; CORRESPONDENTS: BETTY ANN BOWSER; SPENCER MICHES; ELIZABETH FARNSWORTH; PAUL SOLMAN;