The task must lie with Congress. It is Congress that makes the laws that bind the president and the country's agents. Defining terror as that which causes "severe pain and suffering" as both Congress and international law have currently done, leaves far too much room for presidents to, as Bush did, parse defintions of pain. As Eric Posner points out, any attempt to prosecute Bush administration officials for the usage of waterboarding would likely run up against the following defense:
The waterboarders themselves will testify that they received assurances from superiors and lawyers that waterboarding is not illegal, and that they believed that waterboarding was necessary to protect the nation. The superiors, up to Bush himself, will testify that lawyers assured them that waterboarding is not illegal, and that they believed that waterboarding was necessary to protect the nation. The lawyers will testify that they honestly believed that waterboarding is not torture—it caused “pain” but not “severe pain,” in the language of the statute—and that in any event statutes need to be interpreted narrowly to avoid a conflict with the president’s commander-in-chief powers. The jury will believe all these people and it will refuse to convict or, at best, it will hang, prolonging everyone’s agony. It might refuse to convict because it doesn’t believe that anyone has the requisite mens rea; because it doesn’t understand the law; or because (most likely) it just doesn’t believe that people should go to jail when they are trying to protect the nation and the law in question is confusing or ambiguous.This defenses were made possible by a feckless Congress, which outlawed the use of torture but never clearly defined its terms. It is up to Congress as our country's most representative body, as the body charged with creating the law, to define what practices our military and intelligence operatives should be permitted to use to protect the nation. It is not enough for President Obama or his Attorney General-designate to declare "waterboarding is torture," for if there is another serious attack on or threat to this nation, the government will be, as was the Bush administration, under great pressure to take any actions necessary to protect the American people. Congress must put this issue to rest by clearing defining what interrogation techniques are allowable, and what are to be understood to be over the line.