Former White House press secretary Scott McClellan claims President George W. Bush and top aides falsified the truth to make the case for the Iraq war, which he declared unnecessary.
Mr McClellan, the first Bush insider to write a book criticising his former boss and fellow Texan, drew instant fire today from former White House colleagues with whom he was once close.
They questioned why he stayed on the job if he had those feelings and why he never expressed to them.
"If he thinks he's going to ingratiate himself to his critics, he's sorely mistaken, and unfortunately, the only friends he had, he just lost," said Dan Bartlett, who served as White House adviser.
Mr McClellan, in What Happened - Inside the Bush White House and Washington's Culture of Deception, presents himself as a one-time true Mr Bush believer who mistakenly fell in line behind "the campaign to sell the war" in Iraq.
Mr McClellan, who had argued strenuously from the White House podium on why the war was justified, wrote that the decision to go to war in Iraq was a "fateful misstep."
"What I do know is that war should only be waged when necessary, and the Iraq war was not necessary," he said.
Mr McClellan called Mr Bush "a man of personal charm, wit, and enormous political skill," and "plenty smart enough to be president," while sprinkling criticism of him throughout the 341-page book.
"The president had promised himself that he would accomplish what his father had failed to do by winning a second term in office," Mr McClellan wrote.
"And that meant operating continually in campaign mode, never explaining, never apologising, never retreating. Unfortunately, that strategy also had less justifiable repercussions: never reflecting, never reconsidering, never compromising. Especially where Iraq was concerned."
Mr McClellan was replaced as White House press secretary in 2006 by Tony Snow, and Snow gave way to Dana Perino about a year ago.
Ms Perino criticized Mr McClellan.
"Scott, we now know, is disgruntled about his experience at the White House. For those of us who fully supported him, before, during and after he was press secretary, we are puzzled. It is sad - this is not the Scott we knew," she wrote in an e-mail to reporters.
"The book, as reported by the press, has been described to the president. I do not expect a comment from him on it - he has more pressing matters than to spend time commenting on books by former staffers," she said.