In October of 2002, a National Security Estimate summary called a President's Summary, was written specifically for George W. Bush. In that document, Bush was told that despite the buzz that Iraq's procurement of aluminum tubes was "related to a uranium enrichment effort," the State Department's Bureau of Intelligence and Research and the Energy Department's intelligence branch "believe that the tubes more likely are intended for conventional weapons."
This memo, however, did not stop Bush from announcing, three months later, in the State of the Union speech, that Iraq was procuring high-strength aluminum tubes in order to build a nuclear weapon. Later that year, when then-Deputy National Security Advisor Stephen Hadley did a review of documents, and discovered the President's Summary, Karl Rove gathered White House aides together and explained that it would look bad if the American people knew that Bush had been advised that the aluminum tubes were probably harmless.
Hadley was reviewing classified records because of statements made by former ambassador Joseph C. Wilson that Bush's claims about the uranium were not true. George Tenet, who was CIA director at the time, took the blame for the gaffe in the State of the Union address, saying his staff had failed to warn Bush that the uranium claims might not be true. However, two weeks before Bush was given the President's Summary, Tenet had already told him that both the Department of State and the Department of Energy had doubts about the tubes, and that the CIA was also doubtful. In addition, Bush was advised that then-Secretary of State Colin Powell had doubts about the aluminum tubes, also.
Bush clearly knew he was not being accurate when he implied that Iraq was building a nuclear weapon. The State Department knew he was not being accurate. The Department of Energy knew he was not being accurate. The CIA knew he was not being accurate. They all made a circle around him, but eventually, there could not be enough protection for so great an instance of misleading the American people.
For a detailed looked at the history of the memo and everything surrounding it, you may read the complete report in National Journal.