The Vice President stated that he called the President to discuss the rules of engagement for the CAP. He recalled feeling that it did no good to establish the CAP unless the pilots had instructions on whether they were authorized to shoot if the plane would not divert. He said the President signed off on that concept. The President said he remembered such a conversation, and that it reminded him of when he had been an interceptor pilot. The President emphasized to us that he had authorized the shootdown of hijacked aircraft. The Vice President's military aide told us he believed the Vice President spoke to the President just after entering the conference room, but he did not hear what they said. Rice, who entered the room shortly after the Vice President and sat next to him, remembered hearing him inform the President, "Sir, the CAPs are up. Sir, they're going to want to know what to do." Then she recalled hearing him say, "Yes sir." She believed this conversation occurred a few minutes, perhaps five, after they entered the conference room. We believe this call would have taken place sometime before 10:10 to 10:15. Among the sources that reflect other important events of that morning, there is no documentary evidence for this call, but the relevant sources are incomplete. Others nearby who were taking notes, such as the Vice President's chief of staff, Scooter Libby, who sat next to him, and Mrs. Cheney, did not note a call between the President and Vice President immediately after the Vice President entered the conference room. At 10:02, the communicators in the shelter began receiving reports from the Secret Service of an inbound aircraft-presumably hijacked-heading toward Washington. That aircraft was United 93. The Secret Service was getting this information directly from the FAA. The FAA may have been tracking the progress of United 93 on a display that showed its projected path to Washington, not its actual radar return. Thus, the Secret Service was relying on projections and was not aware the plane was already down in Pennsylvania. 
Who said the president signed off on the rules of engagement for the CAP?
President