From the torture memos -- remember these lines were written by suits in the Bush Department of Justice [this is the August 2002 Abu Zubaydah memo]:
... As we explained in the Section 2340A Memorandum, "pain and suffering" as used in Section 2340 is best understood as a single concept, not distinct concepts of "pain" as distinguished from "suffering." See Section 2340A Memorandum at 6 nJ. The waterboard, which inflicts no pain or actual harm whatsoever, does not, in our view inflict "severe pain or suffering." Even if one were to parse the statute more finely to attempt to treat "suffering" as a distinct concept, the waterboard could not be said to inflict severe suffering. The waterboard is simply a controlled acute episode, lacking the connotation of a protracted period of time generally given to suffering. ..
It gets worse --
Based on the information you have provided us, we believe that those carrying out these procedures would not have the specific intent to inflict severe physical pain or suffering. The objective of these techniques is not to cause severe physical pain. First, the constant presence of personnel with medical training who have the authority to stop the interrogation should it appear it is medically necessary indicates that it is not your intent to cause severe physical pain.
The doctors weren't just assisting in the torture -- their presence was deemed to make it legal.