WASHINGTON >> So Jeb Bush now says he would not have invaded Iraq if he knew then what he knows today. Neither would Chris Christie, Ted Cruz, John R. Kasich, Rand Paul, Rick Santorum or Marco Rubio. In fact, Rubio said, “Not only would I not have been in favor of it, President Bush would not have been in favor of it.”

Which raises an interesting question: Would George W. Bush still have authorized the invasion in 2003 had he known that Iraq did not actually have the unconventional weapons that intelligence agencies said it did?

Rubio’s staff said he based his comment on the fact that Bush had expressed regret about the false intelligence he relied on and — since the war was predicated on it — it is reasonable to assume he would have decided differently, if he had known differently.

But in fact, while Bush has said he was sick to learn the intelligence was off base, he has always defended his decision to invade Iraq as the right one, arguing that the world is still better off without Saddam Hussein.

While Bush’s office declined to comment Thursday, this is a question that for years has intrigued former members of Bush’s own team. Top aides like Karl Rove, Ari Fleischer and Richard L. Armitage have suggested that Bush would not have ordered the invasion had he known there were no weapons of mass destruction.

“Would the Iraq war have occurred without WMD?” Rove, the president’s senior adviser, wrote in his memoir, “Courage and Consequence.” “I doubt it.”

In an interview for a history of the Bush administration, Fleischer, who served as press secretary, put it even stronger. “I just don’t think he would have gone to war,” he said. “I think he would have turned up the heat on Saddam, but I don’t think he would have gone to war.”

Armitage, the former deputy secretary of state, said in a separate interview: “I’m convinced that President Bush would not have done it absent WMD.”

But some of the strongest original supporters of the war remain unconvinced. The case against Saddam, they argue, was never solely about unconventional weapons. That was just one of three main elements of the indictment, the others being support of terrorism (he offered bounties to the families of Palestinian suicide bombers, although allegations that he had ties to al-Qaida were disputed by the CIA) and repression of his own people (he was held responsible for killing hundreds of thousands of Iraqis during his long tenure).

“Did the president make the right decision? Obviously, I thought so and still do,” Donald H. Rumsfeld, the former defense secretary, said for the Bush administration history. “I mean, I think he was faced with a whole set of reasons which seemed to me to be persuasive then and now.”

Former Vice President Dick Cheney, asked during an NBC interview a few years ago, said the decision was still the right one. “Oh sure,” he said. “It was sound policy that dealt with a very serious problem and that eliminated Saddam Hussein.”

Some of these war supporters said the administration made a mistake by focusing the public case too intensely on the supposed weapons and leaving the other arguments to the side, as Secretary of State Colin L. Powell did when he went before the United Nations Security Council. Powell focused on the weapons because they were the subject of past Security Council resolutions that Saddam had flouted.

Moreover, it was the possible arsenal of chemical and biological weapons that seemed to make Saddam a threat to the United States, not his human rights record. A year later, when no weapons were found, Powell told The Washington Post that the “absence of a stockpile changes the political calculus” and “changes the answer you get” about whether he would have supported going to war in the first place — comments he tried to walk back after getting in trouble with the White House.

While Bush was still in office, Republicans like Powell were wary of disavowing the invasion, preferring to suggest that the decision was justified given what was believed at the time. Sen. John McCain of Arizona, the party’s eventual 2008 nominee, said the war was still the right thing to have done, and former Gov. Mitt Romney of Massachusetts, an opponent for the nomination, did not argue otherwise. By 2011, though, with Bush in retirement in Dallas and another presidential campaign underway, Romney said that if it had been known there were no weapons, “Why, obviously we would not have gone in.”

That is not a conclusion that Bush has embraced, although he has offered more second thoughts than his vice president has. In his memoir, “Decision Points,” Bush acknowledged two main errors regarding Iraq: the false intelligence and the failure to respond more quickly and forcefully to deteriorating security after Saddam fell.

“No one was more shocked or angry than I was when we didn’t find the weapons,” Bush wrote. “I had a sickening feeling every time I thought about it. I still do.” The false intelligence proved to be “a massive blow to our credibility — my credibility — that would shake the confidence of the American people,” he concluded.

But he did not take that logic to the same place Rubio and now his brother have taken it. Saddam, the former president said, was still a threat to peace who was determined to obtain unconventional weapons, as well as a despot who oppressed his own people.

“Imagine what the world would look like today with Saddam Hussein still ruling Iraq,” he wrote. “He would still be threatening his neighbors, sponsoring terror and piling bodies into mass graves.”

“Instead,” he added, “as a result of our actions in Iraq, one of America’s most committed and dangerous enemies stopped threatening us forever.” And with the troop increase that he ordered that helped turn around the war before he left office, Bush argued that “25 million Iraqis went from living under a dictatorship of fear to seeing the prospect of a peaceful, functioning democracy.”

In another book last year, a short biography of his father called “41,” Bush lamented the deterioration in security in Iraq under President Barack Obama. But he offered no additional regret about the invasion. “One thing is certain: The Iraqi people, the United States and the world are better off without Saddam Hussein in power,” Bush wrote. “I believe the decision that Dad made in 1991 was correct — and I believe the same is true of the decision I made a dozen years later.”

Even if his brother does not.

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