Vision, Strategic and Tactical thinking. Vision: A president will always be a target. Strategic thinking: We need to find where and how the president most likely will be attacked before he is attacked. Tactical thinking: Train to directly protect the President when hot moments occur. It is more than thick doors and heavy arms that protects a president.
Acudo ryu have its sub-division Street Acudo that teaches this way of thinking and acting. Here is a video about the Secret Service that protects the President of The USA.