Feb. 7, 2011— -- More than four years after leaving public life, former Defense Secretary Donald Rumsfeld continues to believe the war in Iraq was worth the effort, and has no apologies for his decision-making in leading the campaigns in Afghanistan and Iraq.
In an exclusive interview with ABC's Diane Sawyer, Rumsfeld concedes that "it's possible" that decisions on how many troops to send into Iraq marked the biggest mistake of the war.
"In a war, many things cost lives," Rumsfeld told Sawyer.
Pressed on the fact that President Bush has written that cutting troop levels in Iraq was "the most important failure in the execution of the war," Rumsfeld called that "interesting."
"I don't have enough confidence to say that that's right. I think that it's possible. We had [an] enormous number of troops ready to go in. They had -- we had off-ramps, if they weren't needed."
"It's hard to know," Rumsfeld continued. "You know, the path you didn't take is always smoother."
Watch Diane Sawyer's Exclusive Interview With Donald Rumsfeld on ABC's "World News With Diane Sawyer" on Monday, Feb. 7, on "Nightline" That Evening, and Feb. 8 on "Good Morning America" and "World News."
The interview -- Rumsfeld's first for television since 2006 -- is tied to the publication of his memoir, "Known and Unknown," this week.
The book spans a half century that took Rumsfeld, now 78, from a back bench as a 30-year-old member of Congress to success in the private and public sectors. He served Republican presidents from Richard Nixon to George W. Bush, including a stint as President Gerald Ford's chief of staff.
Remarkably, he would become both the youngest and oldest man to have served as secretary of defense -- tenures separated by 24 years.
The interview covers the range of Rumsfeld's tenure as Bush's secretary of defense, including harsh interrogation tactics he authorized for use against suspected terrorists, and the scandal at Abu Ghraib prison in Iraq that Rumsfeld himself has described as the low point of his time at the Pentagon.
Reminded in the interview that another former Defense secretary, Robert McNamara, famously said of Vietnam years after the war that "we were wrong, terribly wrong," Rumsfeld rejected the comparison.
"That's not the case with Iraq. That's not the case with Iraq," he said. "I think the world's a better place with Saddam Hussein gone and with the Taliban gone and the al Qaeda out of Afghanistan."
Rumsfeld describes an "incremental" move toward war with Iraq under President Bush, rather than a clear inflection point. He told Sawyer that while the president asked him to update war plans against Iraq shortly after the terror attacks of Sept. 11, 2001, the president never asked him if it was the "right decision."
Inside the Bush administration, Rumsfeld said, "I didn't hear people feeling strongly that he should or shouldn't."
Asked if he turned the conversation inside the administration to Iraq in the wake of 9/11, Rumsfeld said "absolutely not."
"The fact of the matter is, it was raised by somebody up at Camp David [shortly after 9/11] and the president said, 'I don't wanna get into it,'" Rumsfeld said.
Iraq was raised at the Camp David meeting by Paul Wolfowitz, a deputy secretary of Defense who would later become an architect of the Iraq war.