In the beginning, it was a fight over weapons of mass destruction: Did Saddam Hussein have them? Were they an imminent threat? Administration hard-liners voiced no doubt.
"He is, in fact, actively and aggressively seeking to acquire nuclear weapons," said Vice President Dick Cheney on Sept. 8, 2002.
If so, should America go to war? The president sounded convinced later that year, on Oct. 7.
"Facing clear evidence of peril, we cannot wait for the final proof, the smoking gun that could come in the form of a mushroom cloud," he said.
Bush deployed his top diplomat to make the case to the United Nations.
"Let me now turn to those deadly weapons programs," former Secretary of State Colin Powell told the United Nations on Feb. 5, 2003.
In his annual State of the Union speech a month before, President Bush accused Iraq of trying to buy uranium from Africa for weapons fuel.
"The British government has learned that Saddam Hussein recently sought significant quantities of uranium from Africa," Bush told Congress on Jan. 20, 2003.
But the CIA had checked that out a year earlier by sending a secret envoy. His name was Joseph Wilson. And his conclusion: It wasn't true. So Wilson began challenging the crucial evidence the White House was using to justify the invasion.
Flynt Leverett was working in the National Security Council at the time. He quit, in protest, just before the war. He says the Bush team had decided to fight back.
"It was imperative to discredit Wilson, to discredit his argument that the WMD case might not be solid," says Leverett.
Then, Wilson went public — in The New York Times and on "Meet the Press."
"They were using the selective use of facts and intelligence to bolster a decision in the case that had already been made, a decision that had been made to go war," Wilson told "Meet the Press" moderator Tim Russert on July 6, 2003.
Officials point out that Wilson occasionally inflated his role, and on some points, misstated his findings. Sources say, to undermine Wilson, Bush aides told reporters he'd been sent to Africa through the influence of his wife, who worked at the CIA. That led to an investigation into whether they broke the law, either through leaks or in their testimony.
And so the debate over Saddam's weapons has turned into a legal case — and the biggest political crisis of the Bush presidency.