What is waterboarding?
Note the word "suspected."
It's possible for a person who is entirely innocent and has no information whatsoever to be subjected to this form of torture.
People can and do die in the course of waterboarding. The practice is essentially to bring the victim to the edge of drowning, over and over again.
Bush and his henchmen pointedly continue to refuse to ban this practice explicitly.
Theoretically, thanks to George Bush "the Decider", anyone, anywhere, any time, who is suspected of having information related to "terrorism" can be snatched off the street and tortured in this way.
This perhaps more than his lying the US into an illegal, immoral and pointless war and ruining the US economy (a work in progress) may be his ultimate legacy.