This episode's headline: Security Detail; End Game; Busy Signals. The guests include ROBERT SNOW, Former Secret Service Agent; NEIL LIVINGSTONE, Security Consultant; DORIS KEARNS GOODWIN, Historian; PHILIP ELMER- DEWITT, Time Magazine; ELI NOAM, Columbia University; CORRESPONDENTS: BETTY ANN BOWSER; JIM FISHER. Byline: In New York: ELIZABETH FARNSWORTH; In Washington: JAMES LEHRER