A key lesson of the 9/11 decade for presidents and other national security decision makers is the importance of rigorously testing intelligence evidence: poking holes in it, setting out contradictions, figuring out what may have been overlooked or left out. It is essential to distinguish between hard facts and what is an assessment or judgment.

The so-called slam-dunk case that Iraq had weapons of mass destruction illustrates the failure. If anyone should have learned this, it is former president George W. Bush and former vice president Dick Cheney.

Yet in his new memoir, “In My Time,” Cheney shows he has not fully absorbed that lesson when he writes about the administration’s response to the 2007 discovery of a nuclear reactor in Syria that the North Koreans had helped build.

In Cheney’s telling, the evidence showed “a clandestine nuclear reactor, built by two terrorist-sponsoring states.” Given the potential threat, he argued privately to Bush, and later to top national security officials, that the United States should destroy the reactor.

In a National Security Council session that June, he writes, “I again made the case for U.S. military action against the reactor. Not only would it make the region and the world safer, but it would also demonstrate our seriousness with respect to non-proliferation. It would enhance our credibility in that part of the world . . . . But I was the lone voice. After I finished, the president asked, ‘Does anyone here agree with the vice president?’ Not a single hand went up around the room. I had done all I could, and I’m not sure the president’s mind would have been changed if the others had agreed with me.”

He notes with some relish that two months later the Israelis took unilateral action and destroyed the reactor. The clear implication is that Bush and the others had lost their nerve, that they lacked the necessary spine to act as he had recommended.

But accounts from others in these meetings, a public briefing and Bush’s own memoir present a dramatically different picture of the intelligence on the Syrian reactor.

Cheney does not reveal that then-CIA Director Michael V. Hayden had a team working for months to examine the intelligence on the Syrian reactor. Participants at the meetings say that Hayden presented his findings to Bush, Cheney and the others before Cheney made his arguments for a military strike.

According to a principal participant, Hayden made four points, saying: “That’s a reactor. I have high confidence. That Syria and North Korea have been cooperating for 10 years on a nuclear reactor program, I have high confidence. North Korea built that reactor? I have medium confidence. On it is part of a nuclear weapons program, I have low confidence.”

Hayden emphasized the last sentence to underscore his uncertainty. He later told others that he stuck to the intelligence facts and intentionally shaped his presentation that way to discourage a preemptive strike because the intelligence was weak.

According to the CIA, there was no evidence of plutonium reprocessing capability at the site or nearby in that region of Syria, though a reactor of that type would be capable of producing plutonium for nuclear weapons. In addition, there was no identifiable means to manufacture uranium fuel.

Hayden’s declaration of low confidence was, in effect, his anti-slam dunk.

On April 24, 2008, two senior U.S. intelligence officials and a senior White House official briefed reporters on the Syrian reactor after extensive testimony to congressional committees on the issue. One of the briefers restated Hayden’s conclusions and said there was not much physical evidence the reactor was part of a weapons program, so they had only “low confidence” that it was.

His assessment, he said, was that the reactor was planned to be part of a weapons program, but in an apparent reference to the Iraq WMD mistake, the briefer said, “There are lessons learned that are — that came out of previous experience about how to put more rigor into our process. So there’s a difference between evidence and an assessment.”

In his memoir, Bush described the debate about the Syrian reactor, writing that Hayden and the other intelligence experts “had only low confidence of a Syrian nuclear weapons program.”

“Mike [Hayden]’s report clarified my decision,” Bush wrote, adding that he called then-Israeli Prime Minister Ehud Olmert, who wanted the United States to destroy the reactor. Bush says he told Olmert, “I cannot justify an attack on a sovereign nation unless my intelligence agencies stand up and say it’s a weapons program.”

Bush didn’t reveal, however, that his vice president wanted a military strike in the face of “low confidence” intelligence that the reactor was part of a nuclear weapons program. Cheney said he wanted the United States to commit an act of war to send a message, demonstrate seriousness and enhance credibility — a frightening prospect given the doubts.

Two participants in the key National Security Council meeting in June 2007 said that after Cheney, the “lone voice,” made his arguments, Bush rolled his eyes.

At the CIA afterward, the group of specialists who had worked for months on the Syrian reactor issue were pleased they had succeeded in avoiding the overreaching so evident in the Iraq WMD case. So they issued a very limited-circulation memorial coin. One side showed a map of Syria with a star at the site of the former reactor. On the other side the coin said, “No core/No war.”

Bob Woodward is an associate editor of The Post. His assistant, Evelyn M. Duffy, contributed to this column.

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