ISLAMABAD, PAKISTAN – A new videotape that has surfaced in Pakistan threatens a massive attack against the United States by a purported American member of Al Qaeda. It is not yet known if the tape is an authentic Al Qaeda production, but it bears enough resemblance that some experts are taking the tape seriously. The chilling 75-minute digital videotape, seen by a Christian Science Monitor reporter in Pakistan, where it was obtained by ABC News, shows a high degree of sophistication and bears the logo of Al Qaeda's video production house, As-Sahab. On the video, the unknown man's face is...