premise: The White House Visitors Office is responsible for public tours of the White House, for maintaining a facility where the public can obtain information about the White House, and for other White House events such as the White House Easter Egg Roll, Holiday Open Houses, Spring and Fall Garden tours, State Arrival Ceremonies and other special events.
hypothesis: The White House Visitors Office has the duty of protecting the president from harm. 
reason: It says nothing in that statement about them being responsible for the presidents safety or that the Visitors office has any duties directly related to the well being of the president himself. 