There is an old legal maxim,
When the facts are on your side, pound on the facts.
When the law is on your side, pound on the law.
When neither is on your side, pound on the table.
Sometimes this works, but more often it fails. The table is being pounded upon, very heavily and very noisily, but neither the law nor the facts appear to be on the side of the principal pounders.
The Geneva Convention provides various protections for "prisoners of war," as defined in Article 4. In relevant part, Article 4 provides
A. Prisoners of war, in the sense of the present Convention, are persons belonging to one of the following categories, who have fallen into the power of the enemy:
1. Members of the armed forces of a Party to the conflict as well as members of militias or volunteer corps forming part of such armed forces.
2. Members of other militias and members of other volunteer corps, including those of organized resistance movements, belonging to a Party to the conflict and operating in or outside their own territory, even if this territory is occupied, provided that such militias or volunteer corps, including such organized resistance movements, fulfill the following conditions:
(a) That of being commanded by a person responsible for his subordinates;
(b) That of having a fixed distinctive sign recognizable at a distance;
(c) That of carrying arms openly;
(d) That of conducting their operations in accordance with the laws and customs of war.
3. Members of regular armed forces who profess allegiance to a government or an authority not recognized by the Detaining Power.
Such protections are not provided for people not meeting the definitional requirements.
However, it is argued that the portions of the U.S. Code dealing with "torture" are to be read independently of the Geneva Convention and its various protocols. I think this is incorrect. Nevertheless, assuming arguendo a lack of interdependence, water boarding and other forms of "harsh interrogation" still do not seem to violate, or in the the past to have violated, the U.S. Code. 18 U.S.C. Section 2441(d)(1)(A), which defines "torture" as follows:
The act of a person who commits, or conspires or attempts to commit, an act specifically intended to inflict severe physical or mental pain or suffering (other than pain or suffering incidental to lawful sanctions) upon another person within his custody or physical control for the purpose of obtaining information or a confession, punishment, intimidation, coercion, or any reason based on discrimination of any kind. (emphasis added)
In subsection (d)(2), applicable following the 2006 enactment of he Military Commissions Act a few changes are made including that the term "severe" is replaced by "serious,", :
the term “serious physical pain or suffering” shall be applied for purposes of paragraph (1)(B) as meaning bodily injury that involves—