As a former Head of State, the US State Department's Bureau of Diplomatc Security would nominally be "in charge." "Grunt work" will be done by the local Sheriff's office, local Police Dept, and the KHP. I had worked with them a couple of times in the past for various functions in my area. (Bethel College in North Newton has had several foreign dignitaries here as part of a lecture series on World-wide peace initiatives). He will almost certainly have his own security forces as well.
Not sure what frequencies they use. I suppose there is a listing somewhere in the database....n0lqt-.-