It is very clear how Feith and Rumsfeld, by abandoning FM 35-42, the Geneva Conventions and the Constitution of the United States.

From the VF excerpt:
Feith confirms that the logic of the law was not followed with respect to Geneva, rather it deliberately created a legal black hole into which the detainees were meant to fall—and that was the point. “Didn’t the administration’s approach mean that Geneva’s constraints on interrogation couldn’t be invoked by anyone at Guantánamo?” Sands asked Feith. “Oh yes, sure,” Feith replied. “Was that the intended result?” “Absolutely.” Sands writes that he asked again: Under the Geneva Conventions, no one at Guantánamo was entitled to any protection? “That’s the point,” Feith reiterated. As he saw it, either you were a detainee to whom Geneva didn’t apply (al-Qaeda fighters, because they weren’t part of a state); or you were a detainee to whom Geneva applied but whose rights you couldn’t invoke (members of the Taliban, because they hadn’t worn uniforms or insignia). What was the difference for the purpose on interrogation? Sands asked. Feith answered with a certain satisfaction: “It turns out, none. But that’s the point.”

When Sands asks Feith whether he was at all concerned that the Geneva decision might have diminished America’s moral authority, Feith tells Sands, “The problem with moral authority” was “people who should know better, like yourself, siding with the assholes, to put it crudely.”