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.
After serving as defense secretary in the final stretch of the Ford administration, Rumsfeld came back to the Pentagon in January 2001 with a mission to cut the bureaucracy and modernize the military.
That mission changed, however, after Sept. 11, 2001 -- a day when he rushed through smoke-filled corridors inside the Pentagon to aid the wounded. He grabbed a mangled shard of the destroyed airliner that day from the lawn outside the Pentagon, a piece of twisted metal he has had mounted and keeps on display in his office in Washington.
After 9/11, he told Sawyer, "I had to impose a sense of urgency into the department. ... This was the first war of the 21st century."
He added: "There wasn't a guidebook or a map or some program that said, 'Here's how you do this.' We had to figure it out."
Rumsfeld had frank assessments of several of his colleagues and contemporaries. Asked if he admired President George H.W. Bush -- a Republican president he didn't serve under -- Rumsfeld was curt.
"No. No," Rumsfeld said. "No, I was kind of disappointed in him. ... He decided he wanted to leave people with the impression that he didn't want to go to the CIA [in the Ford administration]. And that someone made him go there. And it was probably Rumsfeld or something."
His relationship and sometime rivalry with the first President Bush, he said, left him "amazed" that his son asked him to return to Pentagon post he had left 24 years earlier.
"It shows a lot -- about George W. Bush," he said. "That he's his own man."
Rumsfeld was less impressed by some of the president's closest advisers. Of Condoleezza Rice, President Bush's national security adviser and later secretary of state, he said, "She'd never served in a senior administration position" -- a lack of experience that showed in her lack of organization in putting together critical meetings.
"She'd been an academic. And, you know, a lot of academics like to have meetings," Rumsfeld said. "And they like to bridge differences and get people all to be happy."
Colin Powell, Bush's first secretary of state, "did not, in my view, do a good job of managing the people under him," Rumsfeld said.
"There was a lot of leaking out of the State Department, and the president knew it," he said. "And it was unhelpful. And most of it ended up making the State Department look good. We didn't do that in the Pentagon. I insisted we not do it."
Powell, Rumsfeld said, never spoke up in meetings with the president to raise objections to the Iraq war.
"There's a lot of stuff [in] the press that say Colin Powell was against it. But I never saw even the slightest hint of that," he said.
He said that Powell -- along with other top Bush administration officials and advisers -- truly believed Saddam had weapons of mass destruction at the time of his famous presentation to the United Nations in February 2003. Powell would say in May 2004 that some of the intelligence he based his presentation on was "deliberately misleading."
"My Lord, he's the guy who had more experience than anyone else," Rumsfeld said of Powell. "He worked hard with George Tenet, with Condi Rice. He prepared his speech. He went up to the U.N. He made his case. And he wasn't lying. The idea that he was lying or duped is nonsense."
Rumsfeld acknowledges that he erred in a March 2003 interview with ABC's George Stephanopoulos, when he said that despite the failure to find weapons of mass destruction shortly after the invasion of Iraq, "we know where they are."
Rumsfeld writes that he meant to say that U.S. intelligence agencies knew where "suspect sites" were, not that anyone knew definitively where the actual weapons were. But it was a misstatement Rumsfeld's critics seized on, for the duration of his service in the Bush administration and beyond.
"My goodness, the intelligence was certainly wrong," he told Sawyer.
He wouldn't entertain questions about whether he would have acted differently had he known the truth about the lack of WMDs in Iraq.
"I have no idea. I have no idea," he said. "What you know today can help you on things you're thinking about tomorrow. It can't help you with things you were thinking about back then. Back then there was reasonable confidence that he had these weapons."
Rumsfeld dismissed the criticism he got from a collection of retired military leaders in 2006, as the war effort in Iraq was going poorly. The former officials took the extraordinary step of calling for Rumsfeld's resignation, citing what some viewed as an imperious leadership style as well as missteps in leading the Iraq war.
"It was a group of people who were disgruntled. And I've never worked with most of them. Fact, I'd not met some of them," Rumsfeld said.
Rumsfeld offered no apologies for his notoriously brusque management style, saying he would not accept criticism for asking "tough questions."
"Oh, the poor people, I terrified them. My goodness, come on," Rumsfeld said. "These are people with stars on their shoulders. They're people who are patriots. They're people who've fought battles. And they weren't terrified or intimidated."
He expressed disappointment that Bush also felt he was sometimes too abrupt with military leaders and members of his staff.
"You know, it's too bad," Rumsfeld said. "He believed -- apparently believed -- the mythology that was perpetrated in the press."
Rumsfeld's book also sheds light on personal struggles that sometimes came at moments of great professional challenges.
His son, Nick, was battling drug addiction around the time of 9/11 and had gone missing earlier that summer. Just two weeks after the terrorist attacks, Rumsfeld writes, Bush offered his defense secretary comfort on the subject of his son, during a private meeting in the Oval Office that brought Rumsfeld to tears.
"He reached out and said, you know, 'Tell me about it,' " he said. "And you start talking about it. And it's hard to talk about it, because it's -- a wonderful human being, that you love. And you want it to be better. And he is, God bless him."
The book takes its title from a famous news conference where Rumsfeld lectured the press about the limits of intelligence gathering, musing aloud about "known knowns," "known unknowns," and "unknown unknowns."
Though the locution has been used to mock him at times, Rumsfeld said the phrases are an apt summation of his career and experiences.
"It is a thread that runs through my public service," he said, "that there are things we don't know we don't know. And nobody knows them."
"Proceeds from the sales of Known and Unknown will go to the veterans charities supported by the Rumsfeld Foundation."
"World News with Diane Sawyer" will have more of Sawyer's exclusive interview with Rumsfeld tomorrow on "World News" and on ABCNews.com