The actual smoking gun

From the memo itself comes this obvious but condeming evidence.

C reported on his recent talks in Washington. There was a perceptible shift in attitude. Military action was now seen as inevitable. Bush wanted to remove Saddam, through military action, justified by the conjunction of terrorism and WMD. But the intelligence and facts were being fixed around the policy. The NSC had no patience with the UN route, and no enthusiasm for publishing material on the Iraqi regime's record. There was little discussion in Washington of the aftermath after military action.

From Wikipedia:

On May 5, 2005, Conyers and 88 other members of Congress wrote an open letter to the White House inquiring about the new documents leaked which revealed the secret agreement between the United States and the United Kingdom to attack Iraq in 2002. The Times, a British national newspaper, reported that newly-discovered documents reveal British and U.S. intentions to invade Iraq and leaders of the two countries had "discussed creating pretextual justifications for doing so". The documents go on to say that Blair decided the U.S. would need to "create" conditions to justify the war.

The 88 members of Congress, headed by Representative Conyers, say they seek an inquiry into the matter. The story broke in the United Kingdom, but has not received much coverage in the United States, prompting Conyers to lament: "This should not be allowed to fall down the memory hole during wall-to-wall coverage of the Michael Jackson trial and a runaway bride."