The US already have a sophisticated suite of electronic counter-measures in support of the president's movements (for convoys, etc.) I believe they also have the ability to detect drones though no idea if they have the capabilities to shoot them down specifically (by either kinetic or electronic counter-measures).
Precisely. In the end security forces have to cope with things like grenades through to noxious substances.
The US presidents' car is really only related to a car by the fact it appears to have 4 wheels and looks car shaped. Oh and it's painted Henry Ford black.