As Ronald Reagan took to the road last week, moving briskly from Air Force One to limousines and helicopters, and from them to platforms and podiums, his retinue included a field-grade officer carrying a thick black leather briefcase, who usually walked a few respectful paces behind the President. The officer is one of four, representing each of the four armed services, who are responsible for staying near the President everywhere he goes, every moment of the day and night, switching off in shifts. Their other responsibility: not to drop the briefcase. Hence its irreverent nickname—"the football."
It is, for the...