As his presidential library and museum open, former President George W. Bush said he remains "very comfortable" with perhaps the most controversial decision of his presidency -- the invasion of Iraq -- as he pursues a post-presidency removed from the spotlight but active on a series of core issues.

In a wide-ranging interview that touched on everything from his brother Jeb Bush's presidential prospects, the Republican Party's future, and his new passion for painting, he told ABC News' Diane Sawyer he hopes the library and museum serve as resources for historians to judge him based on the same facts he had access to as president.

That includes his decision to invade Iraq, despite the fact that the world later learned that Saddam Hussein did not have weapons of mass destruction. The museum presents that information directly, Bush said.

"We're just laying out the facts. And that was a fact," Bush said. "I am comfortable in the decision-making process. I think the removal of Saddam Hussein was the right decision for not only our own security but for giving people a chance to live in a free society. But history will ultimately decide that, and I won't be around to see it.

"As far as I'm concerned, the debate is over. I mean, I did what I did. And historians will ultimately judge those decisions."

As the formal dedication of the George W. Bush Presidential Center takes place Thursday, Bush appears at ease with both his much-lower profile and his handling of the major episodes that defined his presidency. President Obama and all four living former presidents, including George W. Bush's father, plan on attending the ceremony just outside Dallas.

The younger Bush's post-presidential efforts are aligned with some of the more popular initiatives of his presidency -- fighting AIDS in Africa and empowering women in the Middle East, for example. The new museum, like Bush's memoir, "Decision Points," focuses intensely on critical periods of his presidency, including 9/11, the run-up to the Iraq War, Hurricane Katrina and the 2008 financial crisis.

As a brand-new grandfather who says he's now painting daily, Bush said those who wonder if he has sleepless nights about the decisions he made as president shouldn't worry.

"No, sleeping pretty well," Bush said. "It's nice of 'em that [they] can be concerned about my sleeping habits, but ... I'm rested. I know I'm rested."

The presidential center, set on a sprawling 23-acre site on the campus of Southern Methodist University, houses the Bush Library and Museum as well as the Bush Institute. The institute, founded in 2009, builds on the principles of the Bush presidency through research and training on economic growth, education reform, global health, human freedom, wounded veterans, and helping women in the Middle East.

"Through the Bush Institute," former first lady Laura Bush said, "we've had the chance to continue to work on the issues we think are so important, that were important to us when George was president and that we want to work on, really, for the rest of our lives."