president of the united states. >> mr. president, when did you discover that two of the subpoenaed white house tapes did not exist? >> let me just respond, if i could, sir, before going to your question. i'll turn left, then come back to the right. i don't want to tilt either way at the moment, as you can be sure. >> well, today another bomb exploded. more trouble about those subpoenaed tapes. >> the 18-minute segment of another of the subpoenaed watergate tapes is missing. >> you can be sure that this kind of a subject is one that is a difficult one to explain. >> technical experts report that the 18-minute gap was caused by erasing and re-recording. >> impeach him now! impeach nixon now! impeach nixon now! >> let me just say this. i want to say this to the television audience because people have got to know whether