From The New York Review of Books:
The vice-presidential search in the spring of 2000 was characteristic of the co-presidency to come in one other way. It involved the collection of information for future use against political rivals. In this case, the rivals were the other potential VPs, among them Lamar Alexander, Chuck Hagel, and Frank Keating. They had been asked to submit exhaustive data concerning friends, enemies, sexual partners, psychological vicissitudes (noting all visits to therapists of any kind), personal embarrassments, and sources of possible slander, plus a complete medical history. Each also signed a notarized letter that gave Cheney the power to request records from doctors without further clearance.
All this information would prove useful in later years. Barton Gellman reveals in Angler that soon after Frank Keating was mentioned as a likely candidate for attorney general, a story appeared in Newsweek about an awkward secret in his past: an eccentric patron had paid for his children's college education. No law had been broken, and nothing wrongly concealed; but the story killed a chance for Keating to be named attorney general; and the leak could only have come from one person. Doubtless most of the secrets in Cheney's possession were the more effective for not being used.
Entire article can be found here.