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President Bush says he refused to "bail out my political party" by withdrawing troops "during the darkest days of Iraq," a decision now lauded by his father in an unprecedented joint interview of both presidents by Brit Hume on "FOX News Sunday."

"During the darkest days of Iraq, people came to me and said, 'You're creating incredible political difficulties for us,'" the current president said as his term draws to a close. "And I said, 'Oh, really? What do you suggest I do?' And some suggested retreat, pull out of Iraq.

"But I had faith that freedom exists in people's souls and therefore, if given a chance, democracy and Iraqi-style democracy could survive and work," the president said. "I didn't compromise that principle for the sake of trying to, you know, bail out my political party."

The president's father, former President George H.W. Bush, became emotional when assessing his son's tenure.

"You can make a tough decision and stay with it," he told his son before turning to Hume in the White House Diplomatic Room. "And he's been tested unlike any other president with 9/11. So he passed the test."

He said political invective has "gotten worse" since his days in the White House, adding: "It's offensive, very offensive."

The younger Bush agreed. "The biggest disappointment in the political process, that's been this kind of bitterness by a few people to the point where they don't want to have a logical discussion or a civil discussion about policy," he said. "They just want to tear you down."

But with the war in Iraq nearly won after years of setbacks, the younger Bush exudes serenity as he wraps up his two terms in the White House. "I'm better than fine -- I am proud of the accomplishments of this administration," he said. "I know I gave it my all for eight years, and I did not sell my soul for the sake of popularity. And so when I get back home and look in the mirror, I will be proud of what I see."

Bush said he was also proud of the CIA, although he acknowledged the agency has leaked intelligence secrets. "There have been disappointing moments when information came out of the agency," he said.

"You can't stop leaks. And you don't know how many people were leaking, but I can assure you, the vast majority of people in the CIA were very cooperative."

Bush said he is planning to write a book about his presidency.

"I'm toying with the idea of maybe describing the toughest decisions I had to make as president, and the context in which I made them," he said. "It is very hard for people to remember what life was like a mere four or five years ago. And it's going to be very important for me to recreate the environment in which I had to make certain decisions, particularly the environment of right after September the 11th, 2001."

Bush conceded that his prosecution of an increasingly unpopular war contributed to the fact that the Republican Party "got whipped in 2008." And he warned that a comeback will be difficult "if the party is viewed as anti-immigrant."

But he said the GOP should remain anti-tax and pro-military. "We shouldn't change our philosophy," he said. "We may want to change our messaging. We definitely want to change messengers. We need a new group of leaders."

He added: "I had one in mind. But he evidently didn't agree with his older brother."

It was a reference to former Florida Gov. Jeb Bush, who announced last week he would not run for a Senate seat.

Unlike his son, the elder President Bush served only one term, leaving him to wonder about "things I'd like to have done" on his "unfulfilled agenda." But he has remained active since leaving the White House, even skydiving well into his golden years. He plans another jump in June, when he will be 85.

"I think he's a nut to jump out of airplane at age 70, 75, 80 and 85," remarked his son, who added: "Actually, I think it's cool."

His dad, who now walks with a cane, agreed. "You don't want to sit around just because you're an old guy, drooling in the corner," the elder Bush said. "Old guys can still do stuff." To which his son quipped: "You can drool and jump at the same time."