"After all, Dr. Kupperman was the Deputy National Security Advisor to the President throughout the period to your inquiry," the letter states. "The same is true, of course, of Ambassador Bolton, who was the National Security Advisor to the President, and who was personally involved in many of the events, meetings, and conversations about which you have already received testimony, as well as many relevant meetings and conversations that have not yet been discussed in the testimonies thus far."