n 1995, Steven Emerson got into a Washington taxi and noticed on the seat an Arabic-language newspaper bearing his picture with a bull's-eye superimposed on it. Shortly thereafter, with death threats from Islamic militants multiplying, Emerson went underground. He changed apartments, varied his routes and stayed away from windows. This is a routine he continues to this day, although since Sept. 11 he has sharply increased his profile. It is rare to turn on a cable news program devoted to Islamic extremism without being confronted with Emerson. After a decade of relative obscurity, he now enjoys the status of a...