But as much as the findings of the reports by Lord Butler and Senate Intelligence Committee undermine the case for war, they may also weaken critics' cases against President Bush and Prime Minister Tony Blair.
So far, both men have escaped any substantial blame for the way they depicted the Iraqi threat.
The Butler report, released Wednesday, echoed the U.S. Senate investigation in concluding that Iraq did not "have significant — if any — stocks of chemical or biological weapons in a state fit for deployment, or developed plans for using them."
But Butler also absolved Blair's government and the intelligence agencies of "deliberate distortion or culpable negligence."
Last week's Senate report did not address whether Bush administration officials had overstated or exaggerated the case for war — a subsequent report will focus on that issue. But the Senate did conclude that political pressure played no role in the assessments of the CIA, although Democrats disagreed with that conclusion.
Blair has weathered three previous inquiries, all of which cleared his government of misusing intelligence on Iraqi weapons of mass destruction as it built a case for war. The prime minister's personal ratings have fallen since the war, and newspapers constantly speculate about the end of his run in power.
Mr. Bush is on firmer ground, but poll numbers in the United States also point to wide public distrust of the war the case for war was made.
The findings of the Butler and Senate reports, however, allow both leaders to claim that while the intelligence preceding the war was imperfect, the outcome was positive.
Blair said he accepted the report's findings and accepted personal responsibility for any errors made.
"I have to accept, as the months have passed, it seems increasingly clear that at the time of invasion Saddam did not have stockpiles of chemical or biological weapons ready to deploy," Blair said.
But, he insisted, "I cannot honestly say I believe getting rid of Saddam was a mistake at all. Iraq, the region, the wider world is a better and safer place without Saddam."
"No one lied, no one made up the intelligence, no one inserted things into dossier against the advice of intelligence services," Blair said.
Mr. Bush made a similar argument on Monday.
"Although we have not found stockpiles of weapons of mass destruction, we were right to go into Iraq," Mr. Bush said. "We removed a declared enemy of America who had the capability of producing weapons of mass murder and could have passed that capability to terrorists bent on acquiring them. In the world after September 11th, that was a risk we could not afford to take."
The Butler report bolstered some of Blair's arguments while undercutting others. It said that Iraq "had the strategic intention of resuming the pursuit of prohibited weapons
programs … was carrying out illicit research and development, and procurement, activities" and "was developing ballistic missiles with a range longer than permitted under relevant United Nations Security Council resolutions."
But the report concluded that the September 2002 dossier prepared by Blair's government on the Iraqi threat pushed its case to the limits of available intelligence.
"Language in the dossier may have left with readers the impression that there was fuller and firmer intelligence behind the judgments than was the case," the report said.
The informality of the procedures within Blair's government for forming policies on the risks posed by Iraq "reduced the scope for informed collective political judgment," the report found.
The report was also highly critical of British intelligence-gathering in Iraq.
"Validation of human intelligence sources after the war has thrown doubt on a high proportion of those sources and of their reports, and hence on the quality of the intelligence assessments received by ministers and officials in the period from summer 2002 to the outbreak of hostilities," it said.
The report acknowledged that its conclusions would probably lead to calls for the resignation of John Scarlett, who as chairman of the Joint Intelligence Committee drew up the dossier. He has since been appointed the chief of MI6, Britain's secret intelligence service.
The report, however, said it hoped Scarlett would stay on. "We have a high regard for his abilities and his record," it said.
Butler's report repeated the assessment of a previous inquiry that the 45-minute claim was potentially misleading because it was not made clear that it referred to battlefield munitions.
Butler said there was a suspicion the 45-minute detail, mentioned four times in the September 2002 dossier, had been included in the dossier because it was "eye-catching."
However, Butler's five-member committee, which interviewed Blair, senior Cabinet figures and key intelligence officials, said that in general intelligence material had been correctly reported.
"We should record in particular that we have found no evidence of deliberate distortion or of culpable negligence," the report said.
"We do regard it as a failing, a serious failing, in the dossier that there were not the warnings which were in the Joint Intelligence Committee assessments about the thinness of the evidence," Butler told a news conference.
The report supported Britain's controversial claim that Iraq sought to purchase uranium from Niger. The U.N. nuclear watchdog, the International Atomic Energy Agency, said documents supporting the uranium claim were forgeries.
But Butler said Britain had intelligence from "several different sources."
"The forged documents were not available to the British government at the time its assessment was made, and so the fact of the forgery does not undermine it," it added.
The Africa claim was apparently what Mr. Bush was referring to in his 2003 State of the Union speech when he said, "The British government has learned that Saddam Hussein recently sought significant quantities of uranium from Africa."