'It is my firm belief, as Director of the United States Secret Service, that using Secret Service protective personnel as witnesses concerning non-criminal activities of a President will substantially undermine, if not destroy, the relationship of trust and confidence that must exist between the Secret Service and the President in order for the Secret Service to successfully fulfill its mission.If our Presidents do not have complete trust in the Secret Service personnel who protect them, they may push away the Service's "protective envelope," thereby making them more vulnerable to assassination."