Former Secretary of Defense Donald Rumsfeld answered questions about his new memoir on Tuesday at the Heritage Foundation in Washington. (Roshan Nebhrajani/Medill News Service)

WASHINGTON — Former Secretary of Defense Donald Rumsfeld said Tuesday he wouldn’t change a thing.

When asked whether he’d do anything differently, the often-criticized Rumsfeld fell silent. Then he answered: “Ya know, I can’t think of anything.”

The 78-year-old Rumsfeld enjoyed a welcoming audience at the conservative Heritage Foundation, discussing his just-published memoir “Known and Unknown” and taking the crowd on a trip through U.S. foreign policy that spans eight decades. Rumsfeld has been in public service for 43 years, often at pivotal moments.

“The title of the book came from a discussion I had with people serving on the ballistic missile threat commission back in the 1990‘s,” Rumsfeld said. “It became quite clear that they could tell us what they knew they knew and they could even on occasion tell us what they knew they didn’t know but they didn’t really address the kinds of things that they didn’t know they didn’t know.”

He first served as Secretary of Defense under President Gerald Ford and then became a divisive figure in his second stint in the job under President George W. Bush when he took the nation into two wars — in Iraq and Afghanistan.

Rumsfeld compared himself to Robert S. McNamara, who served under Presidents John F. Kennedy and Lyndon B. Johnson during a critical time for the war in Vietnam, and former Vice President Dick Cheney, who held the job under President George H.W. Bush and was often seen as the engineer of the strategy in the Persian Gulf War.

Rumsfeld emphasized the need to change the way intelligence is handled, highlighting the historical disconnect between members of the Senate, which must confirm key presidential appointments, and the knowledge of threats to U.S. national security.

“In my confirmation hearing, I thought to myself, [Robert S.] MacNamera was never once asked about Vietnam and [Dick] Cheney was never asked about Iraq when he was getting confirmed and I was never asked about Afghanistan when I was getting confirmed. What does that tell you?,” Rumsfeld said. “The members of the Senate are intelligent people and in no case did they ask that question.”

The discussion quickly led into the progress of the wars in Iraq and Afghanistan.

“President [George W.] Bush ran on the platform of transforming the Department of Defense […] That wasn’t my idea that was his idea,” Rumsfeld said.

Comparing the war in Afghanistan to the Cold War, Rumsfeld emphasized the need to adapt defense strategies to deal with the new style of warfare. He also noted that he knew, when going in, that it would be a long war.

“When 9/11 hit, people said that was the end of the transformation of the Department of Defense. But that was wrong, 9/11 was an incentive to do it,” Rumsfeld said.

President Barack Obama has set a deadline of July for troops to begin pulling out of Afghanistan. Military experts have said the pullout won’t likely conclude until 2014.

The conversation then turned to Rumsfeld’s relationships with other political figures like former Secretary of State Colin Powell and Sen. John McCain, R-Ariz.

Reflecting on Powell’s speech to the United Nations that asserted Iraq had weapons of mass destruction, Rumsfeld said that there were no lies and no “bad information.” The information proved to be false and the Bush administration’s case for going to war in Iraq, which was largely built on this “evidence” of weapons, became a rallying cry for Democrats seeking to win the White House in 2008.

In fact, even Republicans that year criticized Bush as the national sentiment began to turn against continuing to fight long wars in Iraq and Afghanistan.

Rumsfeld made no secret of his disdain for McCain, who was the GOP presidential nominee in 2008. “It just wasn’t a good fit,” Rumsfeld said. “I got tired of him.” The audience responded with laughter.