Untold numbers of high-level terror suspects were subjected to waterboarding and sleep deprivation as part of CIA-led interrogation operations at various agency black sites in Asia, Eastern Europe and the Mideast.
Critics have repeatedly claimed the techniques amounted to torture and violate international war laws. They have also questioned whether the techniques actually generated actual, reliable intelligence.
Supporters of the interrogation operations argue the Obama White House wouldn't have been able to order the killing of Osama bin Laden without the intelligence that the techniques produced during the George W. Bush administration.
During Thursday's hearing, defense panel chief Sen. Carl Levin (D-Mich.) used Preston's comments to get the nominee to weigh in on a Senate report on the Bush-era interrogation program.
The Michigan Democrat grilled Preston on whether he disagreed with the CIA's defense of the interrogation program, in response to the report's findings, drafted by the Senate Intelligence Committee.
The agency's response essentially challenges the Senate intel panel's conclusion that the enhanced interrogation techniques were ineffective in gathering intelligence on al Qaeda and other militant terrorist organizations.
Levin asked Preston, who helped write the agency response during his time at CIA, whether he stood by Langley's response.
"Are there any portions of that response that you disagreed with?" Levin asked the nominee.
In response, Preston said there was nothing "legally objectionable" in the agency's defense of the interrogation program.
"That's the determination I need to make," he said.
"I must say I have to rely on those with far greater familiarity with the report and the record. . . but I accept the conclusions and support the recommendations," Preston added.
That said, Levin warned Preston that "there's some significant differences between . . . many members of the committee and that response," adding the defense panel planned to press further into that CIA defense of the interrogation programs.
"But we'll save that for the record," Levin said.