"I think I was unprepared for war," Bush told ABC News' Charlie Gibson in an interview on "World News."
"In other words, I didn't campaign and say, 'Please vote for me, I'll be able to handle an attack,'" he said. "In other words, I didn't anticipate war. Presidents -- one of the things about the modern presidency is that the unexpected will happen."
Bush, who has been a stalwart defender of the war in Iraq and maintaining U.S. troop presence there, said, in retrospect, the war exceeded his expectations.
"A lot of people put their reputations on the line and said the weapons of mass destruction is a reason to remove Saddam Hussein," Bush said. "It wasn't just people in my administration. A lot of members in Congress, prior to my arrival in Washington, D.C., during the debate on Iraq, a lot of leaders of nations around the world were all looking at the same intelligence."
"I wish the intelligence had been different, I guess," Bush said.
When pressed by Gibson, Bush declined to "speculate" on whether he would still have gone to war if he knew Saddam didn't have weapons of mass destruction.
"That is a do-over that I can't do," Bush said.
Despite failed intelligence and accusations of mismanaging the war, Bush said his decision not to prematurely withdraw troops from Iraq was grounded in his values.
"I listened to a lot of voices, but ultimately, I listened to this voice: I'm not going to let your son die in vain," he said. "I believe we can win. I'm going to do what it takes to win in Iraq."
Bush said that one of his biggest disappointments was the failure to pass a comprehensive bill on immigration reform.
"I firmly believe that the immigration debate really didn't show the true nature of America as a welcoming society," he said. "I fully understand we need to enforce law and enforce borders. But the debate took on a tone that undermined the true greatness of America, which is that we welcome people who want to work hard and support their families."
Reflecting on his time in the Oval Office, Bush said that he hopes to be remembered as a president who made difficult decisions in a principled way and "didn't sell his soul for politics."