Nuclear secrets, China and global espionage--Is it a John Le Carre novel, a serious threat to national security or simply a talking point for Republicans? Some are calling the spy scandal growing out of the Los Alamos nuclear laboratory an equivalent to the worst spying during the Cold War. How has espionage evolved since the K.G.B. butted heads with the C.I.A., the Israeli Mossad and the British M.I.5? Can a University of California academic impact U.S. security the way a Soviet double agent could?