Just as Donald Trump is about to officially become the Republican presidential nominee at next week's convention in Cleveland, CIA Director John Brennan issued a direct warning to the billionaire: he will not reinstate waterboarding even if the president orders him to do so.

"If a president were to order the agency to carry out waterboarding or something else...I can say as long as I'm director of CIA--irrespective of what the president says--I'm not going to be the director of CIA that gives that order," he said at a Wednesday event at the Brookings Institution. "They will have to find another director."

Though Director Brennan explicitly avoided using Trump's name in his comments, the presumptive GOP nominee has been criticized for remarks he's made about torture techniques in the past, proclaiming at a presidential debate in New Hampshire that he would "bring back a hell of a lot worse than waterboarding," an interrogation tactic used to simulate the effects of drowning.

"I know that there have been calls for waterboarding, or worse--whatever else," Director Brennan added. "As long as I'm director of CIA, we are not going to go down that road again."

After a backlash from political opponents, military officers and former cabinet members, Trump reversed his position, telling the Wall Street Journal, "I will not order a military officer to disobey the law. It is clear that as president I will be bound by laws just like all Americans and I will meet those responsibilities."

That was in March. In June, Trump senior adviser Barry Bennett caused more controversy when he mentioned waterboarding in relation to presumptive Democratic nominee Hillary Clinton, referring to her response to the FBI inquiry into the handling of her private email server.

"You couldn't get the truth from Hillary Clinton if you waterboarded her," Bennett said.

But the director said there was once a place for "enhanced interrogation techniques," or EITS, particularly in the immediate aftermath of 9/11. At the same time, though, Brennan explained that there is no reliable way to establish cause and effect between the application of these torture techniques and extracting credible information.

"The agency suffered a great cost because of that program," he said.

Brennan assumed his current position in the CIA in March 2013. Less than a year later, in December 2014, he was left to answer for the use of the techniques during George W. Bush's presidency after the Senate Select Intelligence Committee released a damning review of the agency's earlier practices. President Obama, upon taking office in January 2009, banned the use of EITS, which included other methods, such as sleep deprivation.