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The former president said he still feels "sick about" the fact no weapons of mass destruction were found in Iraq.
His response to Hurricane Katrina could have been quicker, he said, and he should have landed Air Force One two days after the storm instead of viewing the destruction through the plane's window. And he said he didn't see the financial meltdown coming.
The former president appeared in a taped episode of The Oprah Winfrey Show.
Writing the memoir, he said, "was an easy process" that has kept him busy.
"A lot of people don't think I can read, much less write," Bush joked on the program.
The world is better off without Saddam Hussein, Bush said, even though the invasion that toppled the Iraqi leader was based on faulty intelligence about the existence of weapons of mass destruction.
"When we didn't find weapons I felt terrible about it, sick about it and still do, because a lot of the case in removing Saddam Hussein was based upon weapons of mass destruction," Bush said.
He added that Hussein was "equally dangerous" without WMDs.
On Katrina, Bush said he didn't land Air Force One to view the submerged New Orleans up close because he was worried about taking resources away from rescue efforts.
"I shouldn't have flown over and looked. I made a mistake. I should have landed," Bush said. "I didn't realize a picture of me looking out would look like I didn't give a darn."
Continuing to discuss Katrina, Bush said he should have sent federal troops to help with security in New Orleans sooner, but was waiting for authority from Louisiana state government.
Bush flared against critics who called his Katrina response racist. Winfrey reminded him that rapper Kanye West said during a 2005 telethon for hurricane survivors that "George Bush doesn't care about black people."
"That really hurt," Bush said. "You can disagree with my politics, but don't ever accuse me of being a racist. ... I can see how the perception would be Bush didn't care, but to accuse me of being a racist is disgusting."
Bush said he wasn't alone in his failure to foresee the financial meltdown and defended his administration's decision to invest in failing banks in late 2008 to stabilize the financial system.
"I believe it helped save the country," Bush said.
Bush had nothing negative to say about President Barack Obama, whom Winfrey famously supported in 2008.
"I didn't like it when people criticized me," Bush said. "And so you're not going to see me out there chirping away (at Obama). And I want our president to succeed. I love our country."