Imagine that President Bush never disclosed in his 2003 State of the Union address that British intelligence believed that Saddam Hussein was seeking uranium from Africa. Suppose that Colin Powell never argued that aluminum tubes were refined for the use of centrifuges before the U.N. Security Council. What if an Iraqi defector codenamed “Curveball” had not persuaded the CIA that Saddam was building mobile biological weapons labs?

In their new book, “Hubris” (Crown, 463 pages, $25.95), Michael Isikoff and David Corn implicitly ask the reader to indulge these counterfactuals. And in exhaustive reporting they seek to show that in these cases and a few others, where specific intelligence used in the buildup to Operation Iraqi Freedom was wrong, war could have been avoided if a stubborn president had only listened to the dissenters.

The authors don’t go quite that far. But the amount of space they devote to these specific pre-war intelligence errors and the political fight that ensued after the Niger claim was questioned leaves the reader with the impression that President Bush was the first person ever to put Saddam Hussein in the same sentence as weapons of mass destruction and terrorism. “There was no doubt,” they write. “Information from intelligence analysts or other experts in or out of government that contradicted or undermined the operating assumptions of the get-Saddam crowd was ignored or belittled.”

But the “get-Saddam crowd” must be a very wide circle if we are to consider the last 15 years as opposed to the last four. Was President Clinton’s defense secretary, William Cohen, out to “get-Saddam” when he went before the Senate with a vial of ricin poison in one of his presentations on the threat of Iraqi weapons of mass destruction? How about the first chief of the U.N. weapons inspection team, Rolf Ekeus, or the man who replaced him, Richard Butler? Saddam himself boasted as late as 2001 of having a “nuclear fedayeen” force. Mr. Clinton’s national security adviser, Samuel Berger, even admitted at the close of his tenure that the sanctions against Iraq had failed.

The point is that most of the intelligence professionals and politicians who paid attention to Iraq before and after September 11, 2001, reasoned that Iraq was concealing weapons of mass destruction, in large part because Saddam Hussein himself was willing to have his country endure international sanctions instead of cooperating fully with the 16 U.N. Security Council resolutions demanding that he disarm. The authors don’t get around to this point until page 173, in a footnote quoting a former White House speechwriter, Matthew Scully. He says, “The basic argument was that ultimately it was for Saddam Hussein to prove he had no weapons of mass destruction, and without that proof, it was America’s responsibility to act.”

It’s a pity that this context is largely missing from “Hubris” because on the substance of the actual intelligence battles before the war, the reporting is dazzling. Messrs. Corn and Isikoff have unearthed many sources inside the intelligence community, including the CIA’s secretive directorate of operations, that add rich context and nuance to what is by now some of the most well-trodden territory in Washington journalism.

One such underreported episode is how the House majority leader in 2002, Richard Armey, a Texas Republican, had voiced serious doubts at early meetings with the White House. When he was personally briefed on the prewar intelligence by Vice President Cheney, Mr. Armey said in retrospect he would have likely dismissed the presentation entirely had it come from a Democratic White House.

The authors also disclose the Anabasis project, a CIA paramilitary operation comprised of Iraqi exiles aimed at sowing discord and playing dirty tricks in the run-up to the war. At one point the project asked the CIA’s Amman, Jordan, station to sabotage a fleet of cars used by the Iraqi regime, only to be rebuked. Amazingly, much of this information is on the record from the team’s co-leader, John McGuire, who is now retired. It was this Anabasis team that recruited Iraq’s Sufi Muslim leader over a dinner in 2002 at the Marrakesh restaurant in Washington to gain access to some of his followers, some of whom worked closely with the Iraqi dictator.

No review of “Hubris” would be complete without at least mentioning the tome’s biggest scoop, the confirmation that the original leaker of Valerie Plame’s status as a CIA officer was not the Cheney cabal, but rather one of its bureaucratic foes, Richard Armitage. The authors, who spilled as much ink as anyone on this nonstory, deserve credit for following the reporting where it led them, even though an inadvertent leak from a war skeptic renders the initial anti-Bush narrative on the whole affair inoperative.

In this light, it’s hard to imagine that only a year ago most self-described liberals cheered a government investigation that compelled two journalists to turn over their notebooks and tell a grand jury the identity of their own confidential sources. But this book relies extensively on confidential sources, whom the authors thank in the acknowledgements for trusting them “with their confidences.” If leak investigations, the likes of which Washington has endured for the last two years, become the norm, then these sources will have good reason not to trust any of us.