The basis for waterboarding being a crime does not come from any statutes in American law. It comes from the Geneva Conventions' explicit ban on torture, which waterboarding clearly is, and in the Eighth Amendment, which bans the use of "cruel and unusual punishment", which waterboarding clearly is. Being president and violating the constitution is a crime against the country. Bush should be prosecuted for that, too. And for violating the terms of the Geneva Conventions about torture.
I can't imagine how or why anyone would try to argue that waterboarding isn't torture, but I'll go about proving it just to satisfy them.
The relevant portions of the Conventions are in Part 2 of the Third Convention.
"Art 13. Prisoners of war must at all times be humanely treated. Any unlawful act or omission by the Detaining Power causing death or seriously endangering the health of a prisoner of war in its custody is prohibited, and will be regarded as a serious breach of the present Convention. In particular, no prisoner of war may be subjected to physical mutilation or to medical or scientific experiments of any kind which are not justified by the medical, dental or hospital treatment of the prisoner concerned and carried out in his interest.
Likewise, prisoners of war must at all times be protected, particularly against acts of violence or intimidation and against insults and public curiosity.
Measures of reprisal against prisoners of war are prohibited.
Art 14. Prisoners of war are entitled in all circumstances to respect for their persons and their honour.
Women shall be treated with all the regard due to their sex and shall in all cases benefit by treatment as favourable as that granted to men.
Prisoners of war shall retain the full civil capacity which they enjoyed at the time of their capture. The Detaining Power may not restrict the exercise, either within or without its own territory, of the rights such capacity confers except in so far as the captivity requires."
Actions explicitly banned:
1. Physical Mutilation
2. Medical experiments
3. Denial of medical treatment
4. Acts of violence, intimidation, or insults
5. Reprisal
6. Disrespect for their persons and honor
There are more, but 1, 4, and 6 illustrate my points. Waterboarding can easily cause permanent physical damage. Water inhalation can damage the lungs, oxygen deprivation can cause brain damage, and prisoners can DIE from it. Waterboarding is a violent practice, forcibly restraining a person in a painful and frightening position, and then commencing to drown them. The only reason that waterboarding is considered "simulated" drowning, is because they stop before the victim actually dies... and then start it all over. Terror and pain are the results of waterboarding. How the hell is this not torture!?
For the constitutional provisions, an act of torture is a cruel punishment. There is no equivocation on that. It is a violation of the Eighth Amendment, and any government official who caused it to happen is guilty, both of breaking their oath of office to uphold the constitution, and of international law that the United States signed. Bush and his ilk are war criminals. And lest you think me biased, which many of you surely will, if we find out that Obama has done this, string him up, too. Same for Clinton. Same for ANYONE.