Bush/Rumsfeld/Cheney wanted to find links betweel al Qaeda and Iraq, so they could make their case to the American people that invading Iraq was a proper response to 9/11.  They didn't have any evidence of links, but they wanted their Iraq War, so they tried to get that "evidence" out of terrorist suspects….by torture:

A former senior U.S. intelligence official familiar with the interrogation issue said that Cheney and former Defense Secretary Donald H. Rumsfeld demanded that the interrogators find evidence of al Qaida-Iraq collaboration.

"There were two reasons why these interrogations were so persistent, and why extreme methods were used," the former senior intelligence official said on condition of anonymity because of the issue's sensitivity.

"The main one is that everyone was worried about some kind of follow-up attack (after 9/11). But for most of 2002 and into 2003, Cheney and Rumsfeld, especially, were also demanding proof of the links between al Qaida and Iraq that (former Iraqi exile leader Ahmed) Chalabi and others had told them were there."

It was during this period that CIA interrogators waterboarded two alleged top al Qaida detainees repeatedly — Abu Zubaydah at least 83 times in August 2002 and Khalid Sheik Muhammed 183 times in March 2003 — according to a newly released Justice Department document.

Torturing people to get the truth is repulsive.  But torturing people to get them to speak your vision of the truth is repulsive and fucked up.