Interpretations vary, but British documents provide rare insight into the lead-up to war.
The memo's warning to British Prime Minister Tony Blair was stark: his upcoming visit to President Bush's Texas ranch would not be a matter of long barbecues and songs around the campfire.
Instead, the April 2002 visit would involve discussion about a possible war in Iraq. Any decisions taken by the Atlantic allies might prove fateful, warned the memo's writer, British Foreign Secretary Jack Straw.
Mr. Blair's own Labour Party - indeed, the world at large - still needed to be convinced why the threat from Saddam Hussein had suddenly become dire, why an invasion wouldn't contravene international law, and what kind of government might replace the Hussein regime.
"The rewards from your visit to Crawford will be few. The risks are high, both for you and the government," said Mr. Straw.
Two years after a US-led force toppled Mr. Hussein, publication of a series of secret internal British documents known collectively as the "Downing Street memos" is shedding new light on the thinking process in Washington and London in the run-up to war.
To some analysts, these memos document how the White House was intent on war in Iraq only months after the terror attacks of Sept. 11, and manipulated intelligence to fit its preconceptions.
To others, the information in the memos is vague, and their general conclusions are matters that were widely reported at the time.
If nothing else, the memos do provide a rare glimpse into the process of policymaking at top levels, and provide the sort of quotes and conclusions that historians may cite for years to come.
The first internal paper to earn the tag "Downing Street Memo" was published in the Sunday Times of London last month.
This memo summarized a July 23, 2002, meeting of Blair and top advisers. Its most widely reported passages relay the impressions garnered by a senior British intelligence official, Richard Dearlove, on a visit to Washington.