Does a drug-detection dog's physical intrusion on a lawfully stopped car constitute an unreasonable search?

QUESTIONS PRESENTED FOR REVIEW I. Does a drug-detection dog physically intrude upon a constitutionally protected area and therefore conduct an unreasonable search under the Fourth Amendment when it touches the exterior of a lawfully stopped car while sniffing for potential contraband? II. Even if touching the exterior of a lawfully stopped car is a physical intrusion of a constitutionally protected area, are the actions of a drug-detection dog, taken without direction, prompting, or facilitation by officers, attributable to the Government for purposes of the Fourth Amendment?